What is the X in X-mas?
mid-14c., from Old French immoble "immovable, fixed, motionless," from Latin immobilis "immovable" (also, figuratively, "hard-hearted"), from assimilated form of in- "not, opposite of" (see in- (1)) + mobilis (see mobile (adj.)). Hence, immobilism "policy of extreme conservatism" (1949, from French immobilisme).
immobile im·mo·bile (ĭ-mō'bəl, -bēl', -bīl')
Not moving; motionless.