What is the X in X-mas?
late 13c., "from elsewhere, foreign, unknown, unfamiliar," from Old French estrange (French étrange) "foreign, alien," from Latin extraneus "foreign, external," from extra "outside of" (see extra). Sense of "queer, surprising" is attested from late 14c. Stranger, attested from late 14c., never picked up the secondary sense of the adjective. As a form of address to an unknown person, it is recorded from 1817, American English rural colloquial. Meaning "one who has stopped visiting" is recorded from 1520s.
This word generally denotes a person from a foreign land residing in Palestine. Such persons enjoyed many privileges in common with the Jews, but still were separate from them. The relation of the Jews to strangers was regulated by special laws (Deut. 23:3; 24:14-21; 25:5; 26:10-13). A special signification is also sometimes attached to this word. In Gen. 23:4 it denotes one resident in a foreign land; Ex. 23:9, one who is not a Jew; Num. 3:10, one who is not of the family of Aaron; Ps. 69:8, an alien or an unknown person. The Jews were allowed to purchase strangers as slaves (Lev. 25:44, 45), and to take usury from them (Deut. 23:20).