The Collaborative International Dictionary of English v.0.48:

Modest \Mod"est\, a. [F. modeste, L. modestus, fr. modus
   measure. See Mode.]
   1. Restraining within due limits of propriety; not forward,
      bold, boastful, or presumptious; rather retiring than
      pushing one's self forward; not obstructive; as, a modest
      youth; a modest man.
      [1913 Webster]

   2. Observing the proprieties of the sex; not unwomanly in act
      or bearing; free from undue familiarity, indecency, or
      lewdness; decent in speech and demeanor; -- said of a
      woman.
      [1913 Webster]

            Mrs. Ford, the honest woman, the modest wife.
                                                  --Shak.
      [1913 Webster]

            The blushing beauties of a modest maid. --Dryden.
      [1913 Webster]

   3. Evincing modestly in the actor, author, or speaker; not
      showing presumption; not excessive or extreme; moderate;
      as, a modest request; modest joy.
      [1913 Webster]

   Syn: Reserved; unobtrusive; diffident; bashful; coy; shy;
        decent; becoming; chaste; virtuous.
        [1913 Webster]

WordNet (r) 3.0 (2006):

modest
    adj 1: marked by simplicity; having a humble opinion of
           yourself; "a modest apartment"; "too modest to wear his
           medals" [ant: immodest]
    2: not large but sufficient in size or amount; "a modest
       salary"; "modest inflation"; "helped in my own small way"
       [syn: modest, small]
    3: free from pomp or affectation; "comfortable but modest
       cottages"; "a simple rectangular brick building"; "a simple
       man with simple tastes"
    4: not offensive to sexual mores in conduct or appearance [ant:
       immodest]
    5: low or inferior in station or quality; "a humble cottage"; "a
       lowly parish priest"; "a modest man of the people"; "small
       beginnings" [syn: humble, low, lowly, modest,
       small]
    6: humble in spirit or manner; suggesting retiring mildness or
       even cowed submissiveness; "meek and self-effacing" [syn:
       meek, mild, modest]
    7: limited in size or scope; "a small business"; "a newspaper
       with a modest circulation"; "small-scale plans"; "a pocket-
       size country" [syn: minor, modest, small, small-
       scale, pocket-size, pocket-sized]

Moby Thesaurus II by Grady Ward, 1.0:

221 Moby Thesaurus words for "modest":
   Olympian, aloof, altruistic, backward, bashful, becoming,
   betwixt and between, blank, boggling, budget, cheap, chilled,
   chilly, clean, cold, committed, common, consecrated, constrained,
   cool, coy, decent, decorous, dedicated, delicate, demeaning,
   demure, demurring, detached, devoted, diffident, disadvantaged,
   discreet, disinterested, distant, dry, dull, easy, economic,
   economy, elegant, expressionless, fair, fair to middling, fairish,
   faltering, forbidding, frigid, frosty, frugal, guarded, hesitant,
   hesitating, homely, humble, humble-looking, humble-visaged,
   humblest, icy, immaculate, impassive, impersonal, in the shade,
   inaccessible, inconspicuous, indifferent, inexpensive, inferior,
   infra dig, inglorious, innocuous, insipid, introverted, junior,
   lackluster, least, less, lesser, limited, low, low-priced, lower,
   lowest, lowliest, lowly, manageable, mean, mediocre, medium, meek,
   middling, minor, moderate, namby-pamby, nice, nominal, of a kind,
   of a sort, of sorts, offish, ordinary, passable, plain, poor,
   priggish, prim, prissy, proper, prudish, pure, puritanical,
   qualmish, reasonable, reluctant, remote, removed, repressed,
   reserved, respectable, restrained, restricted, reticent, retiring,
   sacrificing, scrupulous, second rank, second string, secondary,
   seemly, self-abasing, self-abnegating, self-abnegatory,
   self-conscious, self-denying, self-devoted, self-effacing,
   self-forgetful, self-immolating, self-neglectful, self-neglecting,
   self-renouncing, self-sacrificing, self-unconscious, selfless,
   sensible, servile, shabby, shoddy, shrinking, shy, silent, simple,
   small, so-so, spotless, squeamish, stainless, standoff,
   standoffish, stickling, straitlaced, stuffy, sub, subaltern,
   subdued, subject, subordinate, subservient, suppressed, teachable,
   tedious, temperate, third rank, third string, timid, timorous,
   token, tolerable, unacquisitive, unaffable, unambitious,
   unapproachable, unaspiring, unassertive, unassuming, unassured,
   unblemished, unboastful, uncongenial, undefiled, undemonstrative,
   underprivileged, understated, undistinguished, unelaborate,
   unembellished, unexaggerated, unexceptional, unexpansive,
   unexpensive, ungenial, unimportant, unimposing, unobtrusive,
   unornamented, unostentatious, unpossessive, unpresuming,
   unpresumptuous, unpretending, unpretentious, unselfish,
   unsparing of self, unsullied, vapid, vulgar, wishy-washy,
   withdrawing, withdrawn, within means, worth the money