Question

the number one how it was pronounced in the middle ages ? 

One was pronounced like the nowadays word on (British) 

 The word Only came from what ? 

we know that -ly in the word only is a suffix, if we delete it to return the word  to its origin, how would it be

???

Only came from On + ly

No, it was Onely, and also the meaning is comprehensible

if we pronounce only, we actually pronounce the number one as it was in the middle ages

the adjective (adverb) of the word one was onely. It was written like that in the early modern ages

Henry VI, 291