"wanting sympathy, unkind," c. 1600, from cold (adj.) + -hearted. Originally in Shakespeare. Compare cold-blooded. Old English had cealdheort (adj.) "cruel." Related: Cold-heartedly; cold-heartedness.
Entries linking to cold-hearted
cold adj.
Old English cald (Anglian), ceald (West Saxon) "producing strongly the sensation which results when the temperature of the skin is lowered," also "having a low temperature," from Proto-Germanic *kaldjon (source also of Old Frisian and Old Saxon kald, Old High German and German kalt, Old Norse kaldr, Gothic kalds "cold"), from PIE root *gel- "cold; to freeze" (source also of Latin gelare "to freeze," gelu "frost," glacies "ice").
Sense of "unmoved by strong feeling" was in late Old English. Meaning "having a relatively low temperature, not heated" is from mid-13c. Sense of "dead" is from mid-14c. Meaning "not strong, affecting the senses only slightly" (in reference to scent or trails in hunting or tracking) is from 1590s; hence the extended sense in seeking-games, "distant from the object of search" (1864).
Cold front in weather is from 1921. Cold sweat is by 1630s. Cold-call (v.) in the sales pitch sense is recorded by 1964 (implied in cold-calling; the noun cold call is by 1953; cold-selling is from 1947). Cold comfort (by 1650s) is "little comfort, something which offers little cheer." Cold-cream "cooling unguent for the skin" is from 1709. To throw cold water on in the figurative sense "discourage by unexpected reluctance or indifference" is from 1808.
Japanese has two words for "cold:" samui for coldness in the atmosphere or environment; tsumetai for things which are cold to touch, and also in the figurative sense, with reference to personalities, behaviors, etc.
-hearted
figurative element in combinations, "at heart," also "having a heart" (of a specified kind), c. 1200, first attested in hard-hearted; see heart (n.). Related: -heartedly.
cold-blooded adj.
also coldblooded; 1590s, of persons, "without emotion, wanting usual sympathies, unfeeling;" of actions, from 1828. The phrase refers to the notion in old medicine that blood temperature rose with excitement. In the literal sense, of reptiles, etc., "having blood very little different in temperature from the surrounding environment," from c. 1600. From cold (adj.) + blood (n.). Related: Cold-bloodedly; cold-bloodedness.