early 14c., "a strike or blow," dialectal variant of Middle English dint, dunt (see dint); sense of "indentation, hollow mark made by a blow or pressure" is by 1560s, apparently by influence of indent.
"make a dent or small hollow in by a blow or pressure," late 14c., from dent (n.). Middle English had dinten, dunten "beat with blows" (mid-13c.), from the earlier form of the noun. Related: Dented; denting.