warm (adj.)youdaoicibaDictYouDict[warm 词源字典]
Old English wearm "warm," from Proto-Germanic *warmaz (cognates: Old Saxon, Old Frisian, Middle Dutch, Old High German, German warm, Old Norse varmr, Gothic warmjan "to warm"), of uncertain origin. On one guess it is from PIE *gwher- (cognates: Sanskrit gharmah "heat;" Old Persian Garmapada-, name of the fourth month, corresponding to June/July, from garma- "heat;" Armenian jerm "warm;" Greek thermos "warm;" Latin formus "warm," fornax "oven;" Old Irish fogeir "heated;" Hittite war- "to burn"). On another guess it is connected to the source of Old Church Slavonic goriti "to burn," varŭ "heat," variti "to cook, boil;" and Lithuanian vérdu "to seethe."

The use of distinct words, based on degree of heat, for warm and hot is general in Balto-Slavic and Germanic, but in other languages one word often covers both (Greek thermos; Latin calidus, French chaud, Spanish caliente). In reference to feelings, etc., attested from late 15c. Of colors from 1764. Sense in guessing games first recorded 1860, from earlier hunting use in reference to scent or trail (1713). Warm-blooded in reference to mammals is recorded from 1793. Warm-hearted first recorded c. 1500.[warm etymology, warm origin, 英语词源]