conk as in conk out, 1918, coined by World War I airmen, perhaps in imitation of the sound of a stalling motor, reinforced by conk (v.) "hit on the head," originally "punch in the nose" (1821), from conk (n.), slang for "nose" (1812), perhaps from fancied resemblance to a conch shell.

However, the American Heritage Dictionary has three different meanings for conk:

conk[sup]1[/sup]

PRONUNCIATION: kŏngk

NOUN: 1a.Slang The head. b. A blow, especially on the head. 2. Chiefly British The human nose.

VERB: Inflected forms: conked, conk·ing, conks

TRANSITIVE VERB: To hit, especially on the head.

INTRANSITIVE VERB: 1. To stop functioning; fail: The engine conked out on the final lap. 2. To fall asleep, especially suddenly or heavily: conked out on the couch watching television. 3. To pass out; faint. 4. To die.

ETYMOLOGY: Origin unknown.

conk[sup]2[/sup]

PRONUNCIATION: kŏngk

NOUN: A hard, shelflike, spore-bearing structure of certain wood-decaying fungi, found on stumps, logs, or trees.