From a presumed earlier *hwīe, from West Germanic *hwiu, from Proto-Germanic *hwī (“with what”), to which the more common instrumental ending *-ō had been added. Cognate with Old High German hwiu (instrumental case of hwaz).
Hwy is Literary Welsh. Colloquial Welsh uses nhw instead.
|Note: Some of these forms may be hypothetical. Not every
possible mutated form of every word actually occurs.