mainmast

noun2

1. •
   The tallest mast of a sailing ship that has more than one mast; particularly a full-rigged ship.

   • 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. — 1789
2. •
   The second-foremost mast of a non-sailing ship with more than one mast.