11th cent. From Latin bonus, from Old Latin duenos.
From Proto-Italic *dwenos 'id.' Of difficult etymology, despite cognates in other Indo-European languages. There is no convincing reconstruction in Proto-Indo-European that would yield *dwe- in Proto-Italic. De Vaan (2014) tentatively hypothesizes *du̯h2-eno-, but this would become **dwano- in Proto-Italic. If the original root in Proto-Indo-European was *dh3u̯o- (from *deh3- "to give;" see dar) then a suffix *-eno- is merely an ad hoc explanation, for aside from this solitary word there is no evidence for the existence of a putative *-eno- (Mayrhofer 1992).
As a surname Bueno, originally given to those whose presence was said to be a good omen.
Asturian bonu, Portuguese bom, Galician bo, Catalan bo, French bon, Italian buono, Aromanian bun, Romanian bun, Sardinian bonu
Faliscan duenas "of the brave," duenom "brave"
The surprising sound shift from Old Latin du- to Latin b- is well documented: duonus "good" > bonus; duellum "war" > bellum.