loco /ˈləʊ.kəʊ/adjective 2verb 2adverb 1noun 3forms 6 adjective2 •(US) Intoxicated by eating locoweed. •(informal) Crazy.It's Cottontail Smith, and he's gone plumb loco! — 1943 verb2 •To poison with the loco plant; to affect with locoism. •(informal) To render insane.They say that he is locoed. The insane asylums of California contain many shepherds. — 1904 adverb1 •A direction in written or printed music to be returning to the proper pitch after having played an octave higher or lower. noun3 •A certain species of Astragalus or Oxytropis, capable of causing locoism. •(informal) Short for locomotive.Small boys in 1963 could have traction engines with real steam coming out of the funnel, and Old Western locos had flashing lights, hooters and cow-pushers. — 1971 •(US, informal) Short for locofoco, in its various senses. formslocoed · locoing · locos · locoes · more loco · most loco