​ SLEEVE (O. Eng. slieve, slyf, a. word allied to “slip,” cf. Dutch sloof, apron), that part of a garment which covers the arm, or through which the arm passes or slips. The pattern of the sleeve is one of the characteristics of fashion in dress, varying in every country and period. Various survivals of the early forms of sleeve are still found in the different types of academic or other robes (q.v.). Where the long hanging sleeve is worn it has, as still in China and Japan, been used as a pocket, whence has come the phrase “to have up one's sleeve,” to have something concealed ready to produce. There are many other proverbial and metaphorical expressions associated with the sleeve, such as “to wear one's heart upon one's sleeve,” “to laugh in one's sleeve,” &c. In technical usage a “sleeve” is a tube into which another tube is inserted, which in the case of small tubes is called a thimble.