What is the X in X-mas?
mid-14c., from Old French suspect "suspicious," from Latin suspectus "suspected, suspicious," past participle of suspicere "look up at, mistrust, suspect," from sub "up to" + specere "to look at" (see scope (n.1)). The notion is of "look at secretly," hence, "look at distrustfully." The verb is attested from late 15c.; the noun meaning "a suspected person" is first recorded 1590s. Related: Suspected; suspecting.