Idioms and Phrases with but good
Emphatically, thoroughly, as in Ruth decided to clean up the whole yard but good. The word but in this colloquialism functions as an intensive. Also see and how.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
Examples from the Web for but good
Till now one with sudden hiss: "But-good Christ-just look-why, the roof's leaning—!"The Lord of the Sea
M. P. Shiel