The Collaborative International Dictionary of English v.0.48:

Part \Part\ (p[aum]rt), n. [F. part, L. pars, gen. partis; cf.
   parere to bring forth, produce. Cf. Parent, Depart,
   Parcel, Partner, Party, Portion.]
   1. One of the portions, equal or unequal, into which anything
      is divided, or regarded as divided; something less than a
      whole; a number, quantity, mass, or the like, regarded
      as going to make up, with others, a larger number,
      quantity, mass, etc., whether actually separate or not; a
      piece; a fragment; a fraction; a division; a member; a
      constituent.
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            And kept back part of the price, . . . and brought a
            certain part and laid it at the apostles'feet.
                                                  --Acts v. 2.
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            Our ideas of extension and number -- do they not
            contain a secret relation of the parts ? --Locke.
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            I am a part of all that I have met.   --Tennyson.
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   2. Hence, specifically:
      (a) An equal constituent portion; one of several or many
          like quantities, numbers, etc., into which anything is
          divided, or of which it is composed; proportional
          division or ingredient.
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                An homer is the tenth part of an ephah. --Ex.
                                                  xvi. 36.
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                A thought which, quartered, hath but one part
                wisdom,
                And ever three parts coward.      --Shak.
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      (b) A constituent portion of a living or spiritual whole;
          a member; an organ; an essential element.
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                All the parts were formed . . . into one
                harmonious body.                  --Locke.
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                The pulse, the glow of every part. --Keble.
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      (c) A constituent of character or capacity; quality;
          faculty; talent; -- usually in the plural with a
          collective sense. "Men of considerable parts."
          --Burke. "Great quickness of parts." --Macaulay.
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                Which maintained so politic a state of evil,
                that they will not admit any good part to
                intermingle with them.            --Shak.
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      (d) Quarter; region; district; -- usually in the plural.
          "The uttermost part of the heaven." --Neh. i. 9.
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                All parts resound with tumults, plaints, and
                fears.                            --Dryden.
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      (e) (Math.) Such portion of any quantity, as when taken a
          certain number of times, will exactly make that
          quantity; as, 3 is a part of 12; -- the opposite of
          multiple. Also, a line or other element of a
          geometrical figure.
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   3. That which belongs to one, or which is assumed by one, or
      which falls to one, in a division or apportionment; share;
      portion; lot; interest; concern; duty; office.
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            We have no part in David.             --2 Sam. xx.
                                                  1.
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            Accuse not Nature! she hath done her part;
            Do thou but thine.                    --Milton.
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            Let me bear
            My part of danger with an equal share. --Dryden.
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   4. Hence, specifically:
      (a) One of the opposing parties or sides in a conflict or
          a controversy; a faction.
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                For he that is not against us is on our part.
                                                  --Mark ix. 40.
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                Make whole kingdoms take her brother's part.
                                                  --Waller.
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      (b) A particular character in a drama or a play; an
          assumed personification; also, the language, actions,
          and influence of a character or an actor in a play;
          or, figuratively, in real life; as, to play the part
          of Macbeth. See To act a part, under Act.
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                That part
                Was aptly fitted and naturally performed.
                                                  --Shak.
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                It was a brute part of him to kill so capital a
                calf.                             --Shak.
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                Honor and shame from no condition rise;
                Act well your part, there all the honor lies.
                                                  --Pope.
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      (c) (Mus.) One of the different melodies of a concerted
          composition, which heard in union compose its harmony;
          also, the music for each voice or instrument; as, the
          treble, tenor, or bass part; the violin part, etc.
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   For my part, so far as concerns me; for my share.

   For the most part. See under Most, a.

   In good part, as well done; favorably; acceptably; in a
      friendly manner; as, to take an act in good part.
      --Hooker.

   In ill part, unfavorably; with displeasure.

   In part, in some degree; partly.

   Part and parcel, an essential or constituent portion; -- a
      reduplicative phrase. Cf. might and main, kith and
      kin, etc. "She was . . . part and parcel of the race and
      place." --Howitt.

   Part of speech (Gram.), a sort or class of words of a
      particular character; thus, the noun is a part of speech
      denoting the name of a thing; the verb is a part of speech
      which asserts something of the subject of a sentence.

   Part owner (Law), one of several owners or tenants in
      common. See Joint tenant, under Joint.

   Part singing, singing in which two or more of the harmonic
      parts are taken.

   Part song, a song in two or more (commonly four) distinct
      vocal parts. "A part song differs from a madrigal in its
      exclusion of contrapuntual devices; from a glee, in its
      being sung by many voices, instead of by one only, to each
      part." --Stainer & Barrett.
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   Syn: Portion; section; division; fraction; fragment; piece;
        share; constituent. See Portion, and Section.
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WordNet (r) 3.0 (2006):

part of speech
    n 1: one of the traditional categories of words intended to
         reflect their functions in a grammatical context [syn:
         part of speech, form class, word class]

Moby Thesaurus II by Grady Ward, 1.0:

28 Moby Thesaurus words for "part of speech":
   adjectival, adjective, adverb, adverbial, adversative conjunction,
   attributive, conjunction, conjunctive adverb,
   coordinating conjunction, copulative, copulative conjunction,
   correlative conjunction, disjunctive, disjunctive conjunction,
   exclamatory noun, form class, form word, function class, gerundive,
   interjection, participle, particle, past participle,
   perfect participle, preposition, present participle,
   subordinating conjunction, verbal adjective