loco

American Heritage® Dictionary of the English Language, Fourth Edition

1. adj. Slang Mad; insane.
2. n. See locoweed.
3. n. See loco disease.
4. v. To poison with locoweed.
5. v. Slang To make insane; craze.
6. adv. Music At the pitch written. Used chiefly as a direction.

Century Dictionary and Cyclopedia

1. n. Same as loco-weed.
2. n. A disease of animals resulting from eating loco-weeds. The brain of the animal is affected; it commonly loses both flesh and strength, and death ensues, though not necessarily soon. See loco-weed.
3. To poison with the loco-weed or crazy-weed.
4. Derived from loco-weed.
5. Hence To make crazy or in any way eccentric: as, he's plumb locoed.
6. n. An abbreviated form of locomotive.

Wiktionary

1. adv. music A direction in written or printed music to return to the proper pitch after having played an octave higher or lower.
2. n. rail transport, informal locomotive
3. adj. colloquial crazy
4. adj. intoxicated by eating locoweed
5. n. botany certain species of Astragalus or Oxytropis, capable of causing locoism.

GNU Webster's 1913

1. adv. (Mus.) A direction in written or printed music to return to the proper pitch after having played an octave higher.
2. n. (Bot.) A plant (Astragalus Hornii) growing in the Southwestern United States, which is said to poison horses and cattle, first making them insane. The name is also given vaguely to several other species of the same genus. Called also loco weed.
3. n. (Bot.) Any one of various leguminous plants or weeds besides Astragalus, whose herbage is poisonous to cattle, as Spiesia Lambertii, syn. Oxytropis Lambertii.
4. v. To poison with loco; to affect with the loco disease; hence (Colloq.), to render insane or mad.
5. n. colloq. A locomotive.
6. adj. Originally Southwestern U. S., now slang Insane; crazy.

WordNet 3.0

1. adj. informal or slang terms for mentally irregular