What is the X in X-mas?
1570s, from Latin inhaerentem (nominative inhaerens), present participle of inhaerere "be closely connected with," literally "adhere to," from in- "in" (see in- (2)) + haerere "to stick" (see hesitation). Related: Inherently.
inherent in·her·ent (ĭn-hēr'ənt, -hěr'-)adj. Occurring as a natural part or consequence.