harnpan has the recorded history: A dialectal Northern English and Scots compound of harn ('brain', from Old English hærn) and pan ('vessel, container'), thus the 'pan' that holds the brain. Morphologically, the word is best read through the components named in the history, with the modern spelling preserving a compound structure rather than a single unanalyzable stem. In present English, the noun sense is "the skull or cranium (dialectal and archaic)", so the historical development ends in a clearly identifiable modern dictionary use. The same base also appears in related forms such as brainpan, harn, and pan. Its semantic neighborhood includes skull, cranium, and brainpan, which helps locate the modern sense without adding a separate etymological claim. The named historical forms include Old English hærn.