What is the X in X-mas?
mid-15c., "to invest with a quality," from Middle French qualifier (15c.) and directly from Medieval Latin qualificare "attribute a quality to; make of a certain quality," from Latin qualis "of what sort?," correlative pronomial adjective (see quality) + facere "to make" (see factitious). Meaning "to limit, modify" is from 1530s. Sense of "be fit for a job" first appeared 1580s. Related: Qualified; qualifying.