Origins
The word 'skull' is a Viking-era borrowing whose exact Norse source has long been debated by etymologists, though its Scandinavian origin is not in doubt. The most commonly cited source is an Old Norse form related to 'skúli,' though some scholars point to Norwegian dialect 'skul' (skull) or connect the word more broadly to the Scandinavian family of words including 'skål' (bowl, cup). What all these forms share is a connection to the concept of a hollow, rounded, shell-like vessel — the skull conceived as the bowl that contains the brain.
Before the Norse word arrived, English speakers used several native terms for the skull. The most vivid was 'brainpan' (Old English 'brægenpanne'), a compound that literally means 'brain-pan' and conceives of the cranium as a cooking vessel holding the brain. 'Heafodpanne' (head-pan) was another option. The more clinical Latin term 'cranium' (from Greek 'kranion') also circulated in learned usage. The Norse loanword gradually displaced these native alternatives in everyday speech, though 'brainpan' survived in literary and dialectal use into the modern period.
The deeper etymology connects 'skull' to the PIE root *(s)kelH-, meaning 'to cut' or 'to split,' which also produced 'shell,' 'scale,' 'shale,' and 'skill' (through the sense of splitting or distinguishing). The conceptual link is the idea of something hollowed out or split open — a shell-like container. This same root produced the Scandinavian word 'skål,' meaning 'bowl' or 'cup,' which is also the standard Scandinavian drinking toast. The connection between skulls and bowls in this word family gave rise to the persistent but false legend that Vikings drank from the skulls of their defeated enemies.
Literary History
This legend appears to originate from a mistranslation. The early Scandinavian poem Krákumál, composed in the voice of the legendary Viking Ragnar Lodbrok, contains the phrase 'drekkum bjór af bragði ór bjúgviðum hausa' — 'we will drink beer from the curved branches of skulls.' Later translators rendered 'bjúgviðum hausa' as 'from the skulls,' when the phrase almost certainly means 'from curved horns' (horns being the 'branches' of an animal skull). The conflation of the skull-bowl word family with this mistranslation cemented the myth in popular culture.
The /sk-/ initial sound, as with so many English words of Norse origin, marks 'skull' as a borrowing that entered the language after Old English had already shifted its native /sk-/ to /ʃ/. The native English reflex of the same root produced 'shell' — another hollow, rounded container — and the two words are thus distant relatives that entered English by different routes: 'shell' through native Anglo-Saxon transmission, 'skull' through Viking-era borrowing.
The word's most famous cultural deployment is in the skull and crossbones symbol, which became associated with piracy in the eighteenth century but was originally used on gravestones and in alchemical texts as a memento mori — a reminder of death. 'Numskull' (also 'numbskull'), meaning a stupid person, dates from the sixteenth century and combines 'numb' with 'skull' to create the image of someone whose brain-case is insensate. 'Skullduggery' — meaning underhanded dealings — is surprisingly unrelated to 'skull'; it derives from Scottish 'sculduddery,' meaning obscenity or fornication, and its resemblance to 'skull' is coincidental.