What is the X in X-mas?
1640s (intransitive), 1753 (transitive), back formation from regurgitation, or else from Medieval Latin regurgitatus, past participle of regurgitare. Meaning "to vomit" first attested 1753. Related: Regurgitated; regurgitating.
regurgitate re·gur·gi·tate (rē-gûr'jĭ-tāt')
v. re·gur·gi·tat·ed, re·gur·gi·tat·ing, re·gur·gi·tates
To rush or surge back.
To cause to pour back, especially to cast up partially digested food.