late Middle English (in the sense 'weight'): from Old French pois, peis (noun), peser (verb), from an alteration of Latin pensum 'weight', from the verb pendere 'weigh'. From the early senses of 'weight' and 'measure of weight' arose the notion of 'equal weight, balance', leading to the extended senses 'composure' and 'elegant bearing'early 20th cent.: from the name of Jean L. M. Poiseuille (1799–1869), French physician
