What is the X in X-mas?
Old English cald (Anglian), ceald (West Saxon) "cold, cool" (adj.), "coldness," from Proto-Germanic *kaldaz (cf. Old Frisian and Old Saxon kald, Old High German and German kalt, Old Norse kaldr, Gothic kalds "cold"), possibly a past participle adjective of *kal-/*kol-, from PIE root *gel-/*gol- "cold" (cf. Latin gelare "to freeze," gelu "frost," glacies "ice").
Meaning "not strong" (in reference to scent) is 1590s, from hunting. Cold front in weather is from 1921. Cold-call in the sales pitch sense first recorded 1972. 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.
c.1300, "coldness," from cold (adj.). Sense in common cold is 1530s, from symptoms resembling those of exposure to cold; cf. earlier senses "indisposition caused by exposure to cold" (early 14c.); "discomfort caused by cold" (c.1300).
A viral infection characterized by inflammation of the mucous membranes lining the upper respiratory passages and usually accompanied by malaise, fever, chills, coughing, and sneezing. Also called coryza, acute rhinitis, common cold, coryza.