What is the X in X-mas?
Old English pere, peru "pear," common West Germanic (cf. Middle Dutch, Middle Low German pere, Old High German pira, bira, Dutch peer), from Vulgar Latin *pera, variant of Latin pira, plural (taken for fem. singular) of pirum "pear," a loan word from an unknown source. It likely shares an origin with Greek apion "pear," apios "pear tree."