Swap, v. i. [Cf. Swap, v. t.] 1. To fall or descend; to rush hastily or violently. C. Richardson (Dict.).
All suddenly she swapt adown to ground. Chaucer.
2. To beat the air, or ply the wings, with a sweeping motion or noise; to flap.
Webster's Dictionary 1913
Swap, v. i. [Cf. Swap, v. t.] 1. To fall or descend; to rush hastily or violently. C. Richardson (Dict.).
All suddenly she swapt adown to ground. Chaucer.
2. To beat the air, or ply the wings, with a sweeping motion or noise; to flap.