(1):

(n.) The stomach.

(2):

(n.) A cavity, or one of the cavities, of an organ, as of the larynx or the brain; specifically, the posterior chamber, or one of the two posterior chambers, of the heart, which receives the blood from the auricle and forces it out from the heart. See Heart.

(3):

(n.) Fig.: Any cavity, or hollow place, in which any function may be conceived of as operating.