A certain species of Astragalus or Oxytropis, capable of causing locoism.

(rail transport, informal) A locomotive.

(transitive) To poison with the loco plant; to affect with locoism.

(transitive, colloquial, by extension) To render insane.

(colloquial) Crazy.

(Southwestern US) Intoxicated by eating locoweed.

(music) A direction in written or printed music to be returning to the proper pitch after having played an octave higher or lower.