main·mast 
(mānməst, -măst′)
(mānməst, -măst′)n.
1. The principal mast of a sailing vessel.
2. The taller mast, whether forward or aft, of a two-masted sailing vessel.
3. The second mast aft on a sailing ship with three or more masts.
4. The lower section of such a mast.