adv

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

adj

• (colloquial) Crazy.
  "It's Cottontail Smith, and he's gone plumb loco!"
• (Southwestern US) Intoxicated by eating locoweed.

verb

• (transitive) To poison with the loco plant; to affect with locoism.
• (transitive, colloquial, by extension) To render insane.
  "They say that he is locoed. The insane asylums of California contain many shepherds."

noun

• (rail transport, informal) A locomotive.
  "A locomotive is, next to a marine engine, the most sensitive thing man ever made; and No. .007, besides being sensitive, was new. The red paint was hardly dry on his spotless bumper-bar, his headlight shone like a fireman’s helmet, and his cab might have been a hard-wood-finish parlour. They had run him into the round-house after his trial—he had said good-bye to his best friend in the shops, the overhead travelling-crane—the big world was just outside; and the other locos were taking stock of him."