chief in size, extent, or importance; principal; leading: the company's main office; the main features of a plan.

sheer; utmost, as strength or force: to lift a stone by main force.

of or relating to a broad expanse: main sea.

Grammar. syntactically independent; capable of use in isolation. Compare dependent (def 4), independent (def 14), main clause.

Nautical. of or relating to a mainmast. noting or pertaining to a sail, yard, boom, etc., or to any rigging belonging to a mainmast. noting any stay running aft and upward to the head of a mainmast: main topmast stay.