mainmast

1. (nautical) The tallest mast of a sailing ship that has more than one mast; particularly a full-rigged ship.Examples: "O, the most piteous cry of the poor souls! sometimes to see ’em, and not to see ’em; now the ship boring the moon with her main-mast, and anon swallowed with yest and froth, as you’ld thrust a cork into a hogshead."; "Then turning to his first Minister, who waited behind him with a white Staff near as tall as the Main-mast of the Royal Soveraign, he observed how contemptible a thing was human Grandeur, which could be mimicked by such diminutive Insects as I […]"; "When we were in the latitude of Martinico, and near making the land, one morning we had a brisk gale of wind, and, carrying too much sail, the main-mast went over the side."

2. (nautical) The second-foremost mast of a non-sailing ship with more than one mast.