handstand

(literally) a short-lived regime / being in power over a very short time

(cooking) fish fillet

(figuratively) Three Musketeers

(linguistics, uncommon) trigrade conjugation / (informal) 3-step process

Malayan night heron

(Buddhism) the supreme perfect enlightenment

(uranography) Winter Triangle - a bright asterism of the northern winter sky. Its corners are the stars Betelgeuse, Procyon, and Sirius.

(uranography) Summer Triangle - a bright asterism of the northern summer sky. Its corners are the stars Altair, Deneb, and Vega.

three-legged race / (idiomatic) cooperating and working together to accomplish a task