POST (5)

Post, v. i. [[Cf. OF. poster. See 4th Post.]] 1. 1. To travel with post horses; figuratively, to travel in haste. “Post seedily to my lord your husband.” Shak.
And post o'er land and ocean without rest. Milton. 2. 2. (Man.) To rise and sink in the saddle, in accordance with the motion of the horse, esp. in trotting.