(1):
(n.) 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.
(2):
(adv.) A direction in written or printed music to return to the proper pitch after having played an octave higher.
(3):
(n.) Any one of various leguminous plants or weeds besides Astragalus, whose herbage is poisonous to cattle, as Spiesia Lambertii, syn. Oxytropis Lambertii.
(4):
(n.) A locomotive.
(5):
(v. t.) To poison with loco; to affect with the loco disease; hence (Colloq.), to render insane or mad.