What is the X in X-mas?
1610s, origin obscure; according to OED it emerged into literary speech from the talk of gardeners and farmers, perhaps ultimately from Old English blæce, blæcðu, a scrofulous skin condition and/or from Old Norse blikna "become pale." Used in a general way of agricultural diseases, sometimes with suggestion of "invisible baleful influence;" hence figurative sense of "anything which withers hopes or prospects or checks prosperity" (1828). Cf. slang blighter. Urban blight attested by 1935.
"afflict with blight," 1660s (implied in blighted), from blight (n.). Figurative use by 1712. Related: Blighted; blighting.