Vexillar \Vex"il*lar\, Vexillary \Vex"il*la*ry\, [Cf. F. vexillaire, L. vexillarius a standard bearer.] 1. Of or pertaining to an ensign or standard. 2. (Bot.) Of or pertaining to the vexillum, or upper petal of papilionaceous flowers. {Vexilary [ae]stivation} (Bot.), a mode of [ae]stivation in which one large upper petal folds over, and covers, the other smaller petals, as in most papilionaceous plants.