wool

Wool comes from Middle English wolle, from Old English wull, tracing back through Proto-West Germanic *wullu and Proto-Germanic *wullō to a Proto-Indo-European root reconstructed as *h₂wĺ̥h₁neh₂.

The spelling shifted over time from wu- to wo- since English generally avoids the letter combination 'wu', giving woll, which was then respelled as wool to better match how it sounded.

It's a doublet of lana (as in lanolin), and shares its ancient root with Welsh gwlân, Latin lāna, and even Russian во́лос (vólos, meaning 'hair'), showing how closely wool and hair were once linked in meaning.