The Collaborative International Dictionary of English v.0.48:
main course \main course\ n. 1. The principal part of a meal. Syn: entree. [PJC] 2. (Nautical) A square mainsail. [WordNet 1.5]WordNet (r) 3.0 (2006):
main course n 1: the principal dish of a meal [syn: entree, main course] 2: a square mainsail