From Longman Dictionary of Contemporary Englishthree-corneredˌthree-ˈcornered adjective [usually before noun] 1 CFhaving three corners2 → three-cornered contest/fight
Examples from the Corpus
three-cornered• This is also true with other three-cornered credit transactions, besides car sales.• Third, after a terrific three-cornered fight, were David Hoskins and David James.• The magistrate put on a black cap, a three-cornered piece of silk.• Whittam Smith might feel he could achieve profits faster in a three-cornered race.• The slave trade involved a three-cornered system of exchange. 