1. A controlled and relaxed way of behaving, even in difficult situations.
2. A calm self-assured dignity; especially, in dealing with social situations.
3. A graceful controlled way of standing, moving, or performing an action.
4. A state of hovering or being in suspension, as from equality or equal distribution of weight.
5. The ability to conduct oneself confidently and comfortably; self-possession.
6. Etymology: "weight, quality of being heavy", later "significance, importance" (mid-15th century), from Old French pois, "weight, balance, consideration"; from Medieval Latin pesum, "weight", from Latin pensum and pendere, "to weigh".

The sense of "steadiness, composure" was first recorded in the 1640's, from the notion of being equally weighted on either side.

The verb is first recorded in the late 14th century, "to have a certain weight", from Old French peser, from Vulgar Latin pesare; from Latin pensare. "to weigh carefully", and pendere, "to weigh".