any external prop or support built to steady a structure by opposing its outward thrusts, esp. a projecting support built into or against the outside of a masonry wall.
any prop or support.
a thing shaped like a buttress, as a tree trunk with a widening base.
a bony or horny protuberance, esp. on a horse's hoof.
—v.t.
to support by a buttress; prop up.
to give encouragement or support to (a person, plan, etc.).