The Collaborative International Dictionary of English v.0.48:

Time signature \Time signature\ (Music)
   A sign at the beginning of a composition or movement, placed
   after the key signature, to indicate its time or meter. Also
   called rhythmical signature. It is in the form of a
   fraction, of which the denominator indicates the kind of note
   taken as time unit for the beat, and the numerator, the
   number of these to the measure.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

time signature
    n 1: a musical notation indicating the number of beats to a
         measure and kind of note that takes a beat [syn: time
         signature, musical time signature]

Moby Thesaurus II by Grady Ward, 1.0:

29 Moby Thesaurus words for "time signature":
   accent, accent mark, bar, cancel, character, custos, direct, dot,
   expression mark, fermata, hold, key signature, lead, ligature,
   mark, measure, metronomic mark, notation, pause, presa, segno,
   sign, signature, slur, swell, symbol, tempo mark, tie, vinculum