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.
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The Collaborative International Dictionary of English v.0.48:

Spelling \Spell"ing\, n.
   The act of one who spells; formation of words by letters;
   orthography.
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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.]
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            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.
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            He was much spelled with Eleanor Talbot. --Sir G.
                                                  Buck.
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   3. To constitute; to measure. [Obs.]
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            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.
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            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.
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            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:

Spelling \Spell"ing\, a.
   Of or pertaining to spelling.
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   Spelling bee, a spelling match. [U.S.]

   Spelling book, a book with exercises for teaching children
      to spell; a speller.

   Spelling match, a contest of skill in spelling words,
      between two or more persons.
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WordNet (r) 3.0 (2006):

spelling
    n 1: forming words with letters according to the principles
         underlying accepted usage

Bouvier's Law Dictionary, Revised 6th Ed (1856):

SPELLING, The art of putting the proper letters in words.
     2. It is a rule that when it appears with certainty what is meant, bad
spelling will not avoid a contract; for example, where a man agreed to pay
thirty pounds, he was held bound to pay thirty pounds; and sentence was
holden to be seventeen. Cro. Jac. 607; 10 Coke, 133, a; 2 Roll. Ab. 147.
     3. Even in an indictment undertood has been holden as understood. 1
Chit. Cr. Law.
     4. A misspelling of a name in a declaration, will not be sufficient to
defeat the plaintiff, on the ground of variance between the writing
produced, and the declaration, if such name be idem sonans; as Kay for Key.
16 East, 110; 2 Stark. 29; Segrave for Seagrave. 2 Str. 889. See Idem
Sonans.