Etymology: < post-classical Latin calidus (where some editions read callidus) (of a horse) having white hair on its forehead (4th cent.; a636 in Isidore), perhaps < the same Indo-European base as Byzantine Greek κηλάδες (plural) (of goats) having a knob on their forehead (recorded in a glossary); compare also Lithuanian kalybas dog having a white circle on its neck. Compare also Umbrian kaleřuf , calersu (both accusative plural masculine), in the same sense (though designating cattle): these forms may have been borrowed from the Latin word. Compare later cale n.²The Latin adjective may have been remodelled after adjectives in -idus -id suffix¹ (compare especially the colour terms albidus albid adj., pallidus pallid adj.).

Etymology: < classical Latin callidus wise from experience, practised, expert, clever, ingenious, crafty, cunning < callēre (see callent adj.) + -idus -id suffix¹.