three-cornered

from WordNet (r) 3.0 (2006)

three-cornered
    adj 1: having three corners; "a three-cornered hat"
    2: involving a group or set of three; "a three-cornered race"

from The Collaborative International Dictionary of English v.0.48

Three-cornered \Three"-cor`nered\, a.
   1. Having three corners, or angles; as, a three-cornered hat.
      [1913 Webster]

   2. (Bot.) Having three prominent longitudinal angles; as, a
      three-cornered stem.
      [1913 Webster]