The Collaborative International Dictionary of English v.0.48:

Routine \Rou*tine"\, n. [F., fr. route a path, way, road. See
   Route, Roterepetition.]
   1. A round of business, amusement, or pleasure, daily or
      frequently pursued; especially, a course of business or
      offical duties regularly or frequently returning.
      [1913 Webster]

   2. Any regular course of action or procedure rigidly adhered
      to by the mere force of habit.
      [1913 Webster]

WordNet (r) 3.0 (2006):

routine
    adj 1: found in the ordinary course of events; "a placid
           everyday scene"; "it was a routine day"; "there's nothing
           quite like a real...train conductor to add color to a
           quotidian commute"- Anita Diamant [syn: everyday,
           mundane, quotidian, routine, unremarkable,
           workaday]
    n 1: an unvarying or habitual method or procedure [syn:
         routine, modus operandi]
    2: a short theatrical performance that is part of a longer
       program; "he did his act three times every evening"; "she had
       a catchy little routine"; "it was one of the best numbers he
       ever did" [syn: act, routine, number, turn, bit]
    3: a set sequence of steps, part of larger computer program
       [syn: routine, subroutine, subprogram, procedure,
       function]

Moby Thesaurus II by Grady Ward, 1.0:

264 Moby Thesaurus words for "routine":
   Indian file, MO, accustomed, act, afterpiece, algorithm, approach,
   arranged, arrangement, array, articulation, assigned, attack,
   automatic, average, banal, bank, beat, beaten, beaten path,
   besetting, bit, boring, bureaucracy, bureaucratism, businesslike,
   buzz, catena, catenation, central, chain, chain reaction, chaining,
   chaser, chinoiserie, cliched, common, concatenation, concord,
   connection, consecution, constant, continuum, conventional, course,
   current, curtain, curtain call, curtain raiser, custom, customary,
   cycle, daily grind, deployment, descent, designated, disposal,
   disposition, divertimento, divertissement, dominant, drill, drone,
   endless belt, endless round, epidemic, epilogue, everyday, exode,
   exodus, expository scene, familiar, fashion, file, filiation,
   finale, form, formal, formation, formula, frequent, frequentative,
   gamut, gradation, grind, groove, guise, habit, habitual, hackneyed,
   harmonious, harmony, hoke act, hum, in hand, interlude,
   intermediary, intermediate, intermezzo, intermission, introduction,
   jog trot, layout, line, line of action, lineage, lines, lineup,
   manner, manner of working, many, many times, marshaling, mean,
   means, mechanical, medial, median, mediocre, medium, method,
   methodical, methodology, middle-of-the-road, middling, mode,
   mode of operation, mode of procedure, moderate, modus operandi,
   monotone, monotonous, nexus, normal, not rare, number,
   of common occurrence, oft-repeated, oftentime, order, ordered,
   orderly, ordinary, organization, pandemic, part, pattern, peace,
   pendulum, performance, perfunctory, periodicity, persistent, piece,
   plain, plan, plenum, popular, powder train, practice, predominant,
   predominating, prevailing, prevalent, procedure, proceeding,
   process, programmed, progression, prologue, proportion, queue,
   quiet, quietude, rampant, range, rank, recurrence, recurrent,
   recurring, red tape, red-tapeism, regnant, regular, regularity,
   reigning, repetitive, reticulation, rife, rotation, rote, round,
   row, ruling, run, run-of-the-mill, running, rut, scale, scene,
   schedule, scheduled, sequence, series, setup, shtick, single file,
   sketch, skit, song and dance, spectrum, squirrel cage,
   stand-up comedy act, standard, steady, stereotyped, string,
   striptease, structure, style, succession, swath, symmetrical,
   symmetry, system, systematic, tack, technique, tedious, the drill,
   the how, the way of, thick-coming, thing, thread, tier, tiresome,
   tone, track, train, tranquillity, treadmill, trite, turn,
   unchanging, uneventful, uniform, uniformity, unimaginative,
   uninteresting, unvaried, unvarying, usage, usual, way,
   well-ordered, well-regulated, well-trodden, well-worn,
   well-worn groove, windrow, wise, wont, wonted



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

subroutine
procedure
routine

    (Or "procedure") A sequence of instructions
   for performing a particular task.  Most programming languages,
   including most machine languages, allow the programmer to
   define subroutines.  This allows the subroutine code to be
   called from multiple places, even from within itself (in which
   case it is called recursive).  The programming language
   implementation takes care of returning control to (just after)
   the calling location, usually with the support of call and
   return instructions at machine language level.

   Most languages also allow arguments to be passed to the
   subroutine, and one, or occasionally more, return values to
   be passed back.

   A function is often very similar to a subroutine, the main
   difference being that it is called chiefly for its return
   value, rather than for any side effects.

   (1996-10-01)