What is the X in X-mas?
late 14c., from Old French frognier "to frown or scowl, snort, turn one's nose up," related to froigne "scowling look," probably from Gaulish *frogna "nostril" (cf. Welsh ffroen "nose"), with a sense of "snort," or perhaps "haughty grimace." Related: Frowned; frowning.
1580s, from frown (v.).