What is the X in X-mas?
late 14c., "action of testing or judging; judicial inquiry," from Old French examinacion, from Latin examinationem (nominative examinatio), noun of action from past participle stem of examinare (see examine). Sense of "test of knowledge" is attested from 1610s.
examination ex·am·i·na·tion (ĭg-zām'ə-nā'shən)
An investigation or inspection for the purpose of diagnosis.