late 14c., pensif, "sad, sorrowful, melancholy;" also "engaged in serious thought, meditative, contemplative;" from Old French pensif "thoughtful, distracted, musing" (11c.), from penser "to think," from Latin pensare "weigh, consider," frequentative of pendere "to hang, cause to hang; weigh; pay" (from PIE root *(s)pen- "to draw, stretch, spin"). Meaning "expressing thoughtfulness with sadness" is from 1540s. Related: Pensively; pensiveness.
late 14c., poisen, "to have (a specified) weight," a sense now obsolete, from Old French poiser, stressed form of peser "to weigh, be heavy; weigh down, be a burden; worry, be a concern," from Vulgar Latin *pesare, from Latin pensare "to weigh carefully, weigh out, counter-balance," frequentative of pendere (past participle pensus) "to hang, cause to hang; weigh; pay" (from PIE root *(s)pen- "to draw, stretch, spin").
The meaning "to weigh, ascertain by weighing or balancing is from 1590s, hence the meaning "to hold or place in equilibrium or balance," from 1630s (compare equipoise). The intransitive sense of "be balanced or suspended," figuratively "to hang in suspense" is by 1847; the passive sense of "to be ready" (for or to do something) is by 1932. Related: Poised; poising. In 15c. a poiser was an official who weighed goods. The secondary sense of "to ponder, consider" in Latin pensare yielded pensive; that sense was occasional, but rare in Middle English poise.
also bellydance, 1883, in a British account of travels in Persia, from belly (n.) + dance (n.). In early use sometimes referred to by the French danse du ventre, which is attested by 1872 in French accounts from the Middle East. It appears as a French term in English by 1883, and its use got a boost from the performances of it at the Paris Exposition of 1889.
We agreed, and made our way to the mimic street called Grand Cairo, where we witnessed the lady contortionist who performs a series of movements, designated with charming frankness on the affiches as "La Danse du Ventre." It might with equal candor be called the Lumbar Wriggle [or] the Pectoral Squirm, for this curious Arab almeh possesses the power of moving any one of her principal sets of muscles quite independently of all the others, and can make any prominent part of her person waggle or surge, while its neighboring lines or curves preserve a statuesque rigidity. [Table Talk, September 1889]
The number of women [in the audience] was ludicrously disproportionate, and the number of American women was noticeable. Some of them seemed slightly pensive, but all were interested. Their large eyes grew larger still. They almost forgot decorum in crowding for a better view, in leaning over the backs of chairs in concentrated absorbed attention. [Scribner's Magazine, January 1890]
The English noun is perhaps a direct translation of the French. As a verb from 1963. Related: Belly-dancer (1922); belly-dancing (n.), 1921.