1. A physical state or sense of being able to maintain bodily balance.
2. The ability to maintain a mental state of calmness and composure.
3. A situation in which opposing forces or factors balance each other and stability is attained.
4. In a physical sense: The condition of equal balance between opposing forces; that state of a material system in which the forces acting upon the system, or those that are taken into consideration, are so arranged that their resultant at every point is zero.
5. The state of equal balance between powers of any kind; equality of importance or effect among the various parts of any complex unity.
6. The condition of suspense or uncertainty produced by equality with the forces of opposing influences; neutrality of judgment or volition.
7. Etymology: from Latin æquilibrium, from æquus, "equal" + libra, "a balance, scale".