n. The act of expanding; expansion, as by heat; a spreading or enlarging in all directions; the state of being expanded or distended; distention.n. Specifically Diffuseness of speech; prolixity; enlargement.n. An abnormal enlargement of an aperture or a canal of the body, or one made for the purposes of surgical or medical treatment. See expansion.n. A dilated part of anything; specifically, in zoology, a dilated portion of an organ or a mark.n. In elasticity, change of volume under stress.