Seriously involved; far advanced. For example, He was in deep with the other merchants and couldn't strike out on his own, or She used her credit cards for everything, and before long she was in deep.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
How to use in deep in a sentence
Gyp, crisping her fingers on the reins, drew-in deep breaths.Beyond | John Galsworthy