What is the X in X-mas?
a subtlety or quibbling point; triviality
Latin quid 'something' + -ity
"a trifling nicety in argument, a quibble," 1530s, from Medieval Latin quidditas "the essence of things," in Scholastic philosophy, "that which distinguishes a thing from other things," literally "whatness," from Latin quid "what," neuter of indefinite pronoun quis "somebody, someone or other" (see who). Sense developed from scholastic disputes over the nature of things. Original classical meaning "real essence or nature of a thing" is attested in English from late 14c.