Wiktionary
adv. (context idiomatic English) To a high degree; very thoroughly; in a most definite manner.
Usage examples of "but good".
In a way the magazines were the best: if he found one with the right kind of pictures, there was nothing in it but good parts.
It was the first time I had used ley lines, and basically the last until I went to college since my dad had tanned my hide but good.
Would you settle for my saying I mean her nothing but good things, Fred?
He isn't old, nor anything bad, but good and kind, and the best friend I've got, next to you.
Lord, so long as my will standeth right and firm in Thee, do with me what Thou wilt, for whatsoever Thou shalt do with me cannot be aught but good.
It sounds like a parent talking to his child, but good business is as basic as that concept.
Candide recoiled for an instant, but good manners made him go forward.
His dialect wasn't perfect, but good enough to pass for someone from another district.