the.com/smartness

means The quality of being quick-witted, sharp in judgment, or cleverly adept — mental agility applied to a situation.

from Built from 'smart,' which in Old English (smeortan) originally meant a sharp, stinging pain — the kind of pain a slap gives. The sense drifted from physical sting to mental sting: a 'smart' remark was one that stung with its cleverness, and a 'smart' person had a mind sharp enough to cut. By adding '-ness,' English turned that sharpness into an abstract quality — the state of having a biting, quick mind, now mostly scrubbed of the original pain.