\An`chy*lo"sis\, Ankylosis \An`ky*lo"sis\, n. [NL., fr. Gr. ?, fr. ?, fr. ? to crook, stiffen, fr. ? crooked: cf. F. ankylose.] 1. (Med.) Stiffness or fixation of a joint; formation of a stiff joint. --Dunglison. 2. (Anat.) The union of two or more separate bones to from a single bone; the close union of bones or other structures in various animals.