polygon, polygonal shape - a closed plane figure bounded by straight sides

acute triangle, acute-angled triangle - a triangle whose interior angles are all acute

equiangular triangle, equilateral triangle - a three-sided regular polygon

isosceles triangle - a triangle with two equal sides

oblique triangle - a triangle that contains no right angle

obtuse triangle, obtuse-angled triangle - a triangle that contains an obtuse interior angle

right triangle, right-angled triangle - a triangle with one right angle

scalene triangle - a triangle with no two sides of equal length

cuneus, wedge, wedge shape - any shape that is triangular in cross section

astrology, star divination - a pseudoscience claiming divination by the positions of the planets and sun and moon

triad, triplet, trio - a set of three similar things considered as a unit

lyre - a harp used by ancient Greeks for accompaniment