I. “+ adjective
Etymology: Latin trilater us (from tri- + later-, latus side) + English -al — more at lateral
1. : having three physical or material sides
a trilateral figure
2. : involving three interests often to the disadvantage of other interested parties
a trilateral agreement
trilateral oligopoly in the market place — G.L.Bach
• tri·laterality (|)trī+ noun
• tri·laterally (ˈ)trī+ adverb
II. noun
: a figure having three sides : triangle