Butment

But·ment

A buttress of an arch; the supporter, or that part which joins it to the upright pier. (Arch.)
The mass of stone or solid work at the end of a bridge, by which the extreme arches are sustained, or by which the end of a bridge without arches is supported. (Masonry)

Butment cheek: the part of a mortised timber surrounding the mortise, and against which the shoulders of the tenon bear.