an abundance of money or wealth.
Origin of deep pockets
First recorded in 1975–80
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
Also, deep pockets. A source of substantial wealth or financial support, as in The college relies on the deep pocket of one particular alumna. This term alludes to money-filled pockets. [Slang; 1970s]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.