The Collaborative International Dictionary of English v.0.48:
overcoat \o"ver*coat`\, n. [Cf. Surcoat.] A coat worn over the other clothing; a greatcoat; a topcoat. [1913 Webster]WordNet (r) 3.0 (2006):
overcoat n 1: a heavy coat worn over clothes in winter [syn: greatcoat, overcoat, topcoat] 2: an additional protective coating (as of paint or varnish) [syn: overcoat, overcoating]