Almost, nearly, approximately, as in Our homework was pretty much finished. This adverbial usage differs from the use of pretty for “considerable” (as in pretty penny). [c. 1800]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.