What is the X in X-mas?
Old English ysope, from Irish Latin hysopus, from Greek hyssopos, a plant of Palestine, used in Jewish purification rites, from Hebrew 'ezobh (cf. Syriac zupha, Arabic zufa).
(Heb. 'ezob; LXX. hyssopos), first mentioned in Ex. 12:22 in connection with the institution of the Passover. We find it afterwards mentioned in Lev. 14:4, 6, 52; Num. 19:6, 18; Heb. 9:19. It is spoken of as a plant "springing out of the wall" (1 Kings 4:33). Many conjectures have been formed as to what this plant really was. Some contend that it was a species of marjoram (origanum), six species of which are found in Palestine. Others with more probability think that it was the caper plant, the Capparis spinosa of Linnaeus. This plant grew in Egypt, in the desert of Sinai, and in Palestine. It was capable of producing a stem three or four feet in length (Matt. 27:48; Mark 15:36. Comp. John 19:29).