pin·nate / ˈpināt; -it/ • adj. Bot. (of a compound leaf) having leaflets arranged on either side of the stem, typically in pairs opposite each other. ∎ Zool. (esp. of an invertebrate animal) having branches, tentacles, etc., on each side of an axis, like the vanes of a feather.DERIVATIVES: pin·nat·ed adj.pin·nate·ly adv.pin·na·tion / piˈnāshən/ n.