Why is the ninth month called September?
1560s, from deface + -ment.
mid-14c., "to obliterate," from Old French desfacier "mutilate, destroy, disfigure," from des- "away from" (see dis-) + Vulgar Latin *facia (see face (n.)). Weaker sense of "to mar, make ugly" is late 14c. in English. Related: Defaced; defacing.