mid-14c., "top of the head (including hair)," presumably from a Scandinavian source (though exact cognates are wanting) related to Old Norse skalli "a bald head," skalpr "sheath, scabbard," from PIE root *skel- (1) "to cut." French scalpe, German, Danish, Swedish skalp are from English. Meaning "head skin and hair as proof of death or a victory trophy" is from c. 1600.
"to cut off (someone's) scalp," 1670s, from scalp (n.), originally in reference to North American Indians. For ticket re-selling sense, see scalper. Related: Scalped; scalping. Compare German skalpern, Danish skalpere, Swedish skalpera. French scalper is from Germanic. Similarity to Latin scalpere "to cut, carve" is accidental.