"to trim, to dress up," late 14c., perhaps a variation of prune (v.),
or from O.Fr. poroindre
"anoint before," and O.Fr. proignier
"round off, prune." O.E. preon
meant "to pin," and probably influenced this word. Due to the popularity of falconry, Words for bird activities were formerly much more precise than today.
"Youre hawke proynith and not pikith and she prenyth not bot whan she begynnyth at hir leggys, and fetcheth moystour like oyle at hir taill." ["Book of St. Albans," 1486]