cold-blooded 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.

Old English blod "blood, fluid which circulates in the arteries and veins," from Proto-Germanic *blodam "blood" (source also of Old Frisian blod, Old Saxon blôd, Old Norse bloð, Middle Dutch bloet, Dutch bloed, Old High German bluot, German Blut, Gothic bloþ), according to some sources from PIE *bhlo-to-, perhaps meaning "to swell, gush, spurt," or "that which bursts out" (compare Gothic bloþ "blood," bloma "flower"), from suffixed form of root *bhel- (3) "to thrive, bloom." But Boutkan finds no certain IE etymology and assumes a non-IE origin.

There seems to have been an avoidance in Germanic, perhaps from taboo, of other PIE words for "blood," such as *esen- (source of poetic Greek ear, Old Latin aser, Sanskrit asrk, Hittite eshar); also *krew-, which seems to have had a sense of "blood outside the body, gore from a wound" (source of Latin cruour "blood from a wound," Greek kreas "meat"), but which came to mean simply "blood" in the Balto-Slavic group and some other languages.

Inheritance and relationship senses (also found in Latin sanguis, Greek haima) emerged in English by mid-13c. The meanings "person of one's family, race, kindred; offspring, one who inherits the blood of another" are late 14c. As the fluid of life (and the presumed seat of the passions), blood has stood for "temper of mind, natural disposition" since c. 1300 and been given many figurative extensions. The slang meaning "hot spark, a man of fire" [Johnson] is from 1560s. Blood pressure is attested from 1862. Blood money is from 1530s; originally money paid for causing the death of another.

Blood type is from 1928. That there were different types of human blood was discovered c. 1900 during early experiments in transfusion. To get blood from a stone "do the impossible" is from 1660s. Expression blood is thicker than water is attested by 1803, in reference to family ties of those separated by distance. New (or fresh) blood, in reference to new members of an organization or group, especially ones bringing new ideas and fresh vigor or strength, is from 1880.

"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.