(military) A hardened shelter, often partly buried or fully underground, designed to protect the inhabitants from falling bombs or other attacks.

(nautical) A compartment for storing coal for the ship's boilers; or a tank for storing fuel oil for the ship's engines.

(rail transport) The coal compartment on a tank engine.

(sports) A hazard on a golf course consisting of a sand-filled hollow and an obstacle used in paintball to block an opposing player's view and field of fire.

(Britain, chiefly historical) A large bin or container for storing coal, often built outdoors in the yard of a house.

(Scotland) A sort of box or chest with a lid that serves as a seat, or slang for a kitchen worktop.

(Britain, slang) One who bunks off; a truant from school.

(US, regional) The menhaden, any of several species of fish in the genera Brevoortia and Ethmidium.

(nautical) Load a vessel with coal or fuel oil for the engine, take a load of coal or fuel oil for the engine, or steal bunker fuel by illicitly siphoning it off.

(transitive, golf) Hit a golf ball into a bunker or place a golfer in the position of having a golf ball in a bunker, and in an idiomatic, informal sense, it means to place someone in a difficult or hindered position.

(transitive, paintball) To fire constantly at (an opponent hiding behind an obstacle), trapping them and preventing them from firing at other players; also, to eliminate (an opponent behind an obstacle) by rushing to the position and firing at extremely close range as the player becomes exposed.

(intransitive) Often followed by down: to take shelter in a bunker or other place.