sulphur.

Hellenised variant of earlier sulpur. Etymology uncertain, but likely related to Proto-Germanic *sweblaz (“sulfur”). *The *sw- in the Germanic term suggests a root *swelp-, which could have arisen as a blend of *selp- (“fat, oil”) and *swel- (“to burn”) or alternatively, be a non-Indo-European Wanderwort. *If the comparison with *sweblaz is set aside, the Latin form can simply be derived from the root *selp-, making it cognate to Proto-Germanic *salbō (“salve, ointment”), Sanskrit सर्पिस् (sarpís, “cleaned melted butter”), सृप्र (sṛprá, “greasy, smooth”), Tocharian B ṣalype (“ointment”), and perhaps Ancient Greek ἔλπος (élpos, “?olive oil, fat”) or ὄλπη (ólpē, “flask for oil”). Per De Vaan, Szemerényi reconstructed an s-stem Proto-Indo-European *sélpos. (For the analogical change of the ending to -ur, compare fulgur; for the phonetic change of *-ol- > -ul-, compare sulcus, and for *-el- > *-ol- > -ul-, compare pulpa.) However, De Vaan finds both the -él- > -ól- and -os > -ur changes to be irregular, and suggests the word alternatively comes from Proto-Italic *solpor, from an r/n-stem Proto-Indo-European *sólpr̥ instead.