the.com/numbskull
a head with a full-time vacancy where a brain should be.
means an insulting term for a stupid or slow-witted person.
from from numb plus skull, first popping up in 17th-century english as a jab at anyone whose head seemed padded rather than wired, later softened by cartoons and slapstick into a near-affectionate insult.
first recordedappeared in print around the 1690s
spelling twinalso written numskull, both still valid
tone shiftwent from harsh insult to comic-strip staple