e·qui·lib·ri·um Audio pronunciation of “equilibrium” ( P ) Pronunciation Key (kw-lbr-m, kw-) n. pl. e·qui·lib·ri·ums or e·qui·lib·ri·a (-r-) 1. A condition in which all acting influences are canceled by others, resulting in a stable, balanced, or unchanging system. 2. Mental or emotional balance; poise. 3. Physics. The state of a body or physical system at rest or in unaccelerated motion in which the resultant of all forces acting on it is zero and the sum of all torques about any axis is...