What is the X in X-mas?
Old English wull, from Proto-Germanic *wulno (cf. Old Norse ull, Old Frisian wolle, Middle Dutch wolle, Dutch wol, Old High German wolla, German wolle, Gothic wulla), from PIE *wele- (cf. Sanskrit urna; Avestan varena; Greek lenos "wool;" Latin lana "wool," vellus "fleece;" Old Church Slavonic vluna, Russian vulna, Lithuanian vilna "wool;" Middle Irish olann, Welsh gwlan "wool"). Figurative expression pull the wool over (someone's) eyes is recorded from 1839, American English.
one of the first material used for making woven cloth (Lev. 13:47, 48, 52, 59; 19:19). The first-fruit of wool was to be offered to the priests (Deut. 18:4). The law prohibiting the wearing of a garment "of divers sorts, as of woollen and linen together" (Deut. 22:11) may, like some other laws of a similar character, have been intended to express symbolically the separateness and simplicity of God's covenant people. The wool of Damascus, famous for its whiteness, was of great repute in the Tyrian market (Ezek. 27:18).