The Collaborative International Dictionary of English v.0.48:

Spell \Spell\, n. [OE. speld, AS. speld a spill to light a
   candle with; akin to D. speld a pin, OD. spelle, G. spalten
   to split, OHG. spaltan, MHG. spelte a splinter, Icel. spjald
   a square tablet, Goth. spilda a writing tablet. Cf.
   Spillsplinter, roll of paper, Spell to tell the letters
   of.]
   A spelk, or splinter. [Obs.] --Holland.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Spell \Spell\, v. t. [imp. & p. p. Spelled; p. pr. & vb. n.
   Spelling.] [AS. spelian to supply another's place.]
   To supply the place of for a time; to take the turn of, at
   work; to relieve; as, to spell the helmsman.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Spell \Spell\, n.[AS. spell a saying, tale, speech; akin to OS.
   & OHG. spel, Icel. spjall,Goth. spill. Cf. Gospel, Spell
   to tell the letters of.]
   1. A story; a tale. [Obs.] "Hearken to my spell." --Chaucer.
      [1913 Webster]

   2. A stanza, verse, or phrase supposed to be endowed with
      magical power; an incantation; hence, any charm.
      [1913 Webster]

            Start not; her actions shall be holy as
            You hear my spell is lawful.          --Shak.
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The Collaborative International Dictionary of English v.0.48:

Spell \Spell\, n.
   1. The relief of one person by another in any piece of work
      or watching; also, a turn at work which is carried on by
      one person or gang relieving another; as, a spell at the
      pumps; a spell at the masthead.
      [1913 Webster]

            A spell at the wheel is called a trick. --Ham. Nav.
                                                  Encyc.
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   2. The time during which one person or gang works until
      relieved; hence, any relatively short period of time,
      whether a few hours, days, or weeks.
      [1913 Webster]

            Nothing new has happened in this quarter, except the
            setting in of a severe spell of cold weather.
                                                  --Washington.
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   3. One of two or more persons or gangs who work by spells.
      [R.]
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            Their toil is so extreme that they can not endure it
            above four hours in a day, but are succeeded by
            spells.                               --Garew.
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   4. A gratuitous helping forward of another's work; as, a
      logging spell. [Local, U.S.]
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Spell \Spell\, v. t. [imp. & p. p. Spelledor Spelt; p. pr. &
   vb. n. Spelling.] [OE. spellen, spellien, tell, relate, AS.
   spellian, fr. spell a saying, tale; akin to MHG. spellen to
   relate, Goth. spill?n.e Spell a tale. In sense 4 and those
   following, OE. spellen, perhaps originally a different word,
   and from or influenced by spell a splinter, from the use of a
   piece of wood to point to the letters in schools: cf. D.
   spellen to spell. Cf. Spell splinter.]
   1. To tell; to relate; to teach. [Obs.]
      [1913 Webster]

            Might I that legend find,
            By fairies spelt in mystic rhymes.    --T. Warton.
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   2. To put under the influence of a spell; to affect by a
      spell; to bewitch; to fascinate; to charm. "Spelled with
      words of power." --Dryden.
      [1913 Webster]

            He was much spelled with Eleanor Talbot. --Sir G.
                                                  Buck.
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   3. To constitute; to measure. [Obs.]
      [1913 Webster]

            The Saxon heptarchy, when seven kings put together
            did spell but one in effect.          --Fuller.
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   4. To tell or name in their proper order letters of, as a
      word; to write or print in order the letters of, esp. the
      proper letters; to form, as words, by correct orthography.
      [1913 Webster]

            The word "satire" ought to be spelled with i, and
            not with y.                           --Dryden.
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   5. To discover by characters or marks; to read with
      difficulty; -- usually with out; as, to spell out the
      sense of an author; to spell out a verse in the Bible.
      [1913 Webster]

            To spell out a God in the works of creation.
                                                  --South.
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            To sit spelling and observing divine justice upon
            every accident.                       --Milton.
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The Collaborative International Dictionary of English v.0.48:

Spell \Spell\, v. i.
   1. To form words with letters, esp. with the proper letters,
      either orally or in writing.
      [1913 Webster]

            When what small knowledge was, in them did dwell,
            And he a god, who could but read or spell. --Dryden.
      [1913 Webster]

   2. To study by noting characters; to gain knowledge or learn
      the meaning of anything, by study. [Obs.]
      [1913 Webster]

            Where I may sit and rightly spell
            Of every star that heaven doth shew,
            And every herb that sips the dew.     --Milton.
      [1913 Webster]

WordNet (r) 3.0 (2006):

spell
    n 1: a psychological state induced by (or as if induced by) a
         magical incantation [syn: enchantment, spell, trance]
    2: a time for working (after which you will be relieved by
       someone else); "it's my go"; "a spell of work" [syn: go,
       spell, tour, turn]
    3: a period of indeterminate length (usually short) marked by
       some action or condition; "he was here for a little while";
       "I need to rest for a piece"; "a spell of good weather"; "a
       patch of bad weather" [syn: while, piece, spell,
       patch]
    4: a verbal formula believed to have magical force; "he
       whispered a spell as he moved his hands"; "inscribed around
       its base is a charm in Balinese" [syn: spell, magic
       spell, magical spell, charm]
    v 1: orally recite the letters of or give the spelling of; "How
         do you spell this word?" "We had to spell out our names for
         the police officer" [syn: spell, spell out]
    2: indicate or signify; "I'm afraid this spells trouble!" [syn:
       spell, import]
    3: write or name the letters that comprise the conventionally
       accepted form of (a word or part of a word); "He spelled the
       word wrong in this letter" [syn: spell, write]
    4: relieve (someone) from work by taking a turn; "She spelled
       her husband at the wheel"
    5: place under a spell [ant: unspell]
    6: take turns working; "the workers spell every four hours"

Moby Thesaurus II by Grady Ward, 1.0:

280 Moby Thesaurus words for "spell":
   Jonah, access, act for, add up to, alchemy, allure, alternate,
   amount to, appeal, argue, arsis, attraction, augur, bad influence,
   be construed as, beat, becharm, beguile, bespeak, betoken, bewitch,
   bewitchery, bewitching, bit, bode, bout, break, breath, breathe,
   breather, breathing place, breathing space, breathing spell,
   breathing time, captivate, captivation, carry away, cast a spell,
   chance, change places with, charm, cigarette break, circle,
   circuit, clarify, cocktail hour, coffee break, conjuration,
   connote, course, cover, crowd out, curse, cut out, cycle, day,
   delineate, denote, diastole, displace, divination, divine,
   do a hitch, do a stint, do a tour, do time, double for, downbeat,
   downtime, draw, duration, elucidate, enchant, enchanting,
   enchantment, enforced respite, enlist, enrapture, enravish,
   enthrall, entrance, evil eye, evil genius, evil star, express,
   fascinate, fascination, fateful moment, fetishism, fill in for,
   fit, folklore, foretoken, formula, ghost, ghostwrite, glamour, go,
   gramarye, halt, happy hour, have a go, have tenure, hex, hint,
   hold office, hoodoo, hour, hypnotize, ill wind, imply, import,
   incantation, indicate, infatuate, influence, inning, innings,
   instant, intend, interlude, intermission, interval, intrigue, jinx,
   juju, jujuism, juncture, kairos, keep a watch, lay off, letup,
   lie by, look like, lore, lull, lure, magic, magnetism,
   malevolent influence, malocchio, mean, mesmerism, mesmerize,
   minute, moment, moment of truth, natural magic, necromancy, obeah,
   omen, opportunity, orthographize, outspell, patch, pause, period,
   pinch-hit, place, point, point to, popular belief, portend,
   prefigure, pregnant moment, preindicate, presage, presign,
   presignal, presignify, pretypify, promise, psychological moment,
   pull, pulse, re-up, recess, reenlist, refer to, relay, relief,
   relieve, replace, represent, respite, rest, revolution, rotation,
   round, run, rune, say, season, seizure, series, serve time,
   shamanism, shift, sign up, signify, sorcery, sortilege, space,
   span, specify, spell backward, spell off, spell out, spellbind,
   spellbinding, spellcasting, stage, stand for, stand in for, stay,
   stint, streak, stretch, subrogate, substitute for, succeed,
   suggest, supersede, superstition, superstitiousness, supplant,
   surcease, suspension, swap places with, syllabize, syllable,
   symbolize, sympathetic magic, systole, take over, take turns,
   tea break, tenure, term, thaumaturgia, thaumaturgics,
   thaumaturgism, thaumaturgy, thesis, theurgy, time, time at bat,
   time lag, time off, time out, token, tour, tour of duty, trace out,
   tradition, trance, transport, trick, turn, typify, understudy for,
   upbeat, vamp, vampirism, voodoo, voodooism, wanga, watch, whack,
   whammy, wheel, whet, while, white magic, witch, witchcraft,
   witchery, witchwork, wizardry, write out



The Jargon File (version 4.4.7, 29 Dec 2003):

spell
 n.

    Syn. incantation.


The Free On-line Dictionary of Computing (30 December 2018):

incantation
spell

   Any particularly arbitrary or obscure command that one must
   mutter at a system to attain a desired result.  Not used of
   passwords or other explicit security features.  Especially
   used of tricks that are so poorly documented that they must be
   learned from a wizard.  "This compiler normally locates
   initialised data in the data segment, but if you mutter the
   right incantation they will be forced into text space."