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1.Of or pertaining to an ensign or standard.
2.(Bot.) Of or pertaining to the vexillum, or upper petal of papilionaceous flowers.
Vexilary æstivation
(Bot.) a mode of æstivation in which one large upper petal folds over, and covers, the other smaller petals, as in most papilionaceous plants.
Webster's Revised Unabridged Dictionary, published 1913 by G. & C. Merriam Co.