nonchalant adj.

a prefix used freely in English and meaning "not, lack of," or "sham," giving a negative sense to any word, 14c., from Anglo-French noun-, from Old French non-, from Latin non "not, by no means, not at all, not a," from Old Latin noenum "not one" (*ne oinom, from PIE root *ne- "not" + PIE root *oi-no- "one, unique"). In some cases perhaps from Middle English non "not" (adj.), from Old English nan (see not). "It differs from un- in that it denotes mere negation or absence of the thing or quality, while un- often denotes the opposite of the thing or quality" [Century Dictionary].

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."

"coolness, indifference, unconcern," 1670s, from French nonchalance (13c.), from nonchalant "careless" (see nonchalant).