Emily Dickinson Lexicon

PREEN, v.t. [Scot. proyne, prunyie; Chaucer, proine. This word is probably the same as the foregoing, denoting the use of the beak in cleaning and composing the feathers. So pikith, in Chaucer, is from pike, pick. He kembith him; he proinith him and pikith. – Cant. Tales, 9885. If not, the word may be contracted from the Fr. provigner, to propagate vines by laying cuttings in the ground.]

To clean, compose and dress the feathers, as fowls, to enable them to glide more easily through the air or water. For this purpose they are furnished with two glands on their rump, which secrete an oily substance into a bag, from which they draw it with the bill and spread it over their feathers. – Bailey. Encyc.