MAIN - The tallest mast on a ship.

MAINSHEET - Sail control line that allows the most obvious effect on mainsail trim.

MAN OVERBOARD - When a seaman has gone overboard

MARLINSPIKE - A tool for opening the strands of a rope while splicing.

MAST - A vertical pole on a ship which supports sails or rigging.

MESS - An dining area aboard ship.

MIKE - Letter M in the Marine Radio Alphabet.

MIZZENMAST - The aft mast on a ship.

MOORING - An arrangement for securing a marine vessel to a mooring buoy or a pier.

MONKEY FIST - a ball woven out of line used to heave a line.

MOOR - to attach a boat to a mooring buoy or post.