a closed plane figure having three sides and three angles.

a flat triangular piece, usually of plastic, with straight edges, used in connection with a T square for drawing perpendicular lines, geometric figures, etc.

any three-cornered or three-sided figure, object, or piece

a triangle of land.

a musical percussion instrument that consists of a steel triangle, open at one corner, that is struck with a steel rod.

a group of three; triad.

a situation involving three persons, esp. one in which two of them are in love with the third.

( initial capital letter ) Astronomy . the constellation Triangulum.

adjective

deltoid , deltoidal , pyramidal , pyriform , triangular , trigonal

noun

pyramid , set square