mainmast

noun Nautical.

1. the second mast from forward in any ship having two or more masts, except for a yawl, ketch, or dandy.
2. the larger forward mast of a yawl, ketch, or dandy.
3. the sole mast of any of various ships, as sloops or cutters.

noun

1. nautical the chief mast of a sailing vessel with two or more masts, being the foremast of a yawl, ketch, or dandy and the second mast from the bow of most others

n.16c., from main (adj.) + mast (n.1).