But″tress (�), n. [OE. butrasse, boterace, fr. F. bouter to push; cf. OF. bouteret (nom. sing. and acc. pl. bouterez) buttress. See Butt an end, and cf. Butteris.] 1. (Arch.) A projecting mass of masonry, used for resisting the thrust of an arch, or for ornament and symmetry.
☞ When an external projection is used merely to stiffen a wall, it is a pier.
2. Anything which supports or strengthens. “The ground pillar and buttress of the good old cause of nonconformity.” South.
Flying buttress. See Flying buttress.