alla breve

from WordNet (r) 3.0 (2006)

alla breve
    n 1: a musical time signature indicating two or four half notes
         to a measure

from The Collaborative International Dictionary of English v.0.48

Alla breve \Al`la bre"ve\ [It., according to the breve.] (Old
   Church Music)
   With one breve, or four minims, to measure, and sung faster
   like four crotchets; in quick common time; -- indicated in
   the time signature by ?.
   [1913 Webster]