The Collaborative International Dictionary of English v.0.48:

Dozen \Doz"en\ (d[u^]z"'n), n.; pl. Dozen (before another
   noun), Dozens (d[u^]z"'nz). [OE. doseine, dosein, OF.
   doseine, F. douzaine, fr. douze twelve, fr. L. duodecim; duo
   two + decem ten. See Two, Ten, and cf. Duodecimal.]
   1. A collection of twelve objects; a tale or set of twelve;
      with or without of before the substantive which follows.
      "Some six or seven dozen of Scots." "A dozen of shirts to
      your back." "A dozen sons." "Half a dozen friends."
      --Shak.
      [1913 Webster]

   2. An indefinite small number. --Milton.
      [1913 Webster]

   A baker's dozen, thirteen; -- called also a long dozen.
      [1913 Webster]

WordNet (r) 3.0 (2006):

dozen
    adj 1: denoting a quantity consisting of 12 items or units [syn:
           twelve, 12, xii, dozen]
    n 1: the cardinal number that is the sum of eleven and one [syn:
         twelve, 12, XII, dozen]

Moby Thesaurus II by Grady Ward, 1.0:

51 Moby Thesaurus words for "dozen":
   L, Sexagesima, boxcar, boxcars, duodecimo, eighty, eleven, fifteen,
   fifty, five and twenty, fortnight, forty, four and twenty,
   fourscore, fourscore and ten, fourteen, half a hundred, long dozen,
   ninety, nonagenarian, octogenarian, quindecennial, quindecim,
   quindecima, quindene, score, septuagenarian, seventy, sexagenarian,
   sexagenary, sexagesimo-quarto, sixteen, sixteenmo, sixty,
   sixty-four, sixty-fourmo, teens, thirteen, thirty-two,
   thirty-twomo, threescore, threescore and ten, twelve, twelvemo,
   twenty, twenty-five, twenty-four, twenty-fourmo, two dozen,
   two weeks, twoscore