Poster \Post"er\, n.1. A large bill or placard intended to be posted in public places.
2. One who posts bills; a billposter.
Source: Webster's Revised Unabridged Dictionary (1913)
Poster \Post"er\, n.1. One who posts, or travels expeditiously; a courier. ``Posters of the sea and land.'' --Shak.
2. A post horse. ``Posters at full gallop.'' --C. Lever.