\▐ ja-kәt\ n [ME jaket, fr. MF jacquet, dimin. of jaque short jacket, fr. jacque peasant, fr. the name Jacques James] (15c) (1) A woven or felted tubular sleeve for covering and shrinking on a machine roll. (2) A short coat. (3) In polymer manufacture, an external shell around a reaction vessel. For example, jacketed vessels are used when heat-transfer medium is circulated around the vessel. (Elsevier's textile dictionary. Vincenti R (ed). Elsevier Science and Technology Books, New York, 1994).