early 15c., "weight, quality of being heavy," later "significance, importance" (mid-15c.), from O.Fr. pois "weight, balance, consideration," from M.L. pesum "weight," from L. pensum, noun use of neuter pp. of pendere "to weigh" (see pendant
). The sense of "steadiness, composure"
first recorded 1640s, from notion of being equally weighted on either side (1550s). The verb is first recorded late 14c., "to have a certain weight," from O.Fr. peser, from V.L. pesare, from L. pensare "to weigh carefully," freq. of pendere (pp. pensus) "to weigh." Passive sense of "to be ready" (to do something) is from 1932.