(1):

(n.) A bone of the carpus at the base of the first metacarpal, or thumb.

(2):

(n.) A plane figure bounded by four right lines, of which no two are parallel.

(3):

(n.) A region on the ventral side of the brain, either just back of the pons Varolii, or, as in man, covered by the posterior extension of its transverse fibers.