The Collaborative International Dictionary of English v.0.48:

Diminutive \Di*min"u*tive\, a. [Cf. L. deminutivus, F.
   diminutif.]
   1. Below the average size; very small; little.
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   2. Expressing diminution; as, a diminutive word.
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   3. Tending to diminish. [R.]
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            Diminutive of liberty.                --Shaftesbury.
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The Collaborative International Dictionary of English v.0.48:

Diminutive \Di*min"u*tive\, n.
   1. Something of very small size or value; an insignificant
      thing.
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            Such water flies, diminutives of nature. --Shak.
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   2. (Gram.) A derivative from a noun, denoting a small or a
      young object of the same kind with that denoted by the
      primitive; as, gosling, eaglet, lambkin.
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            Babyisms and dear diminutives.        --Tennyson.
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   Note: The word sometimes denotes a derivative verb which
         expresses a diminutive or petty form of the action, as
         scribble.
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WordNet (r) 3.0 (2006):

diminutive
    adj 1: very small; "diminutive in stature"; "a lilliputian chest
           of drawers"; "her petite figure"; "tiny feet"; "the
           flyspeck nation of Bahrain moved toward democracy" [syn:
           bantam, diminutive, lilliputian, midget,
           petite, tiny, flyspeck]
    n 1: a word that is formed with a suffix (such as -let or -kin)
         to indicate smallness

Moby Thesaurus II by Grady Ward, 1.0:

81 Moby Thesaurus words for "diminutive":
   Lilliputian, affectionate name, baby, baby-sized, bantam, banty,
   button, byname, chit, cognomen, cognominal, compact, duodecimo,
   elfin, epithetic, featherweight, fingerling, formal, handy,
   honorific, hypocoristic, in name only, infinitesimal, lightweight,
   lilliputian, little, micro, microscopic, midget, mini, miniature,
   miniaturized, minikin, minimal, minnow, minny, minuscule, minute,
   mouse, nickname, nominal, nominative, nubbin, peewee, pet name,
   petite, pocket, pocket-sized, pony, pygmy, quasi, runt,
   self-called, self-christened, self-styled, shrimp, slip, small,
   small fry, small-scale, snip, snippet, so-called, sobriquet,
   soi-disant, subminiature, teensy-weensy, teeny, teeny-weeny, tiny,
   tit, titular, toy, twelvemo, undersized, vest-pocket, wart, wee,
   weeny, wisp, would-be