What is the X in X-mas?
c.1400, from Latin constrictionem (nominative constrictio), noun of action from past participle stem of constringere "compress" (see constrain).
constriction con·stric·tion (kən-strĭk'shən)n.
The act of constricting or the state of being constricted.
A feeling of tightness or pressure, as in the chest.
A constricted or narrow part.