scalp, n. /skalp/
Related to “scallop.” The word “scalp” originally referred to (and still does in Scotland) a patch of bare ground or rock, due to its resemblance to the shells of scallops. From that, bald patches on men’s heads were called “scalp” due to their resemblance to the bare patches of ground. Eventually, all of the skin under a person’s hair was called “scalp.”
The word “scalpel” turns out to be unrelated, which has lost etymologists many bar bets over the years.