"hot, burning; ardent," 1590s, from Latin calidus "warm," from PIE root *kele- (1) "warm."
Entries linking to calid
*kele- 1
kelə-, Proto-Indo-European root meaning "warm." It forms all or part of: caldera; calid; Calor; caloric; calorie; calorimeter; cauldron; caudle; chafe; chauffeur; chowder; coddle; lee; lukewarm; nonchalant; scald (v.) "afflict painfully with hot liquid or steam."
It is the hypothetical source of/evidence for its existence is provided by: Sanskrit carad- "harvest," literally "hot time;" Latin calor "heat," calidus "warm," calere "be hot;" Lithuanian šilti "become warm," šilus "August;" Old Norse hlær, Old English hleow "warm."