To make or become deep or deeper.(verb-transitive)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "deepen" in a sentence
"If you read him with attention, Williams will expand your mind, will set it on things wondrous and permanent, will make the world you live in deepen because of the new-perceived order."
"She watched the puzzled expression deepen on Olga's face."
"Odes are recited to the mysterious ways financial elites "deepen" markets and make them more efficient -- how they even out prices."