What is the X in X-mas?
mid-14c., from stem of Old French restreindre "press, push together; curb, bridle; bandage" (12c.), from Latin restringere "draw back tightly, confine, check" (see restriction). Related: Restrained; restraining.
That which we restrain we keep within limits; that which we restrict we keep within certain definite limits; that which we repress we try to put out of existence. [Century Dictionary, 1902]