What is the X in X-mas?
Old English þurst, from West Germanic *thurstus (cf. Old Saxon thurst, Frisian torst, Dutch dorst, Old High German and German durst), from Proto-Germanic *thurs-, from PIE root *ters- "dry" (see terrain). Figurative sense of "vehement desire" is attested from c.1200.
Old English þyrstan (see thirst (n.)); the figurative sense of the verb was present in Old English. Related: Thirsted; thirsting.
A sensation of dryness in the mouth and throat related to a need or desire to drink.
The desire or need to drink.