in deep

Idioms

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 .
in deep water . Also, in over one's head . In trouble, with more difficulties than one can manage, as in The business was in deep water after the president resigned , or I'm afraid Bill got in over his head . These metaphoric expressions transfer the difficulties of being submerged to other problems. The first appears in Miles Coverdale's 1535 translation of the Book of Psalms (68:13): “I am come into deep waters.” The second, which also can signify being involved with more than one can understand, dates from the 1600s. Also see over one's head .

Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

"When you're out in deep space by the Moon, and you are listening to a video they recorded for you before you launch. That's something," the Canadian astronaut told a press conference.

From Barron's • Apr. 9, 2026

The rock layer where the wrinkles formed originated in deep ocean water, nearly 600 feet below the surface.

From Science Daily • Apr. 3, 2026

Masoud Pezeshkian said the "cowardly assassination" had left Iran "in deep mourning", after Israel said on Wednesday it had killed Khatib in an air strike.

From BBC • Mar. 18, 2026

Sent on a far-off mission to save the world from a mysterious threat, he discovers that he may not be alone in deep space.

From The Wall Street Journal • Mar. 15, 2026

Although frightened someone might still be hunting me, I fell fast asleep in deep peace, thanking God again.

From "March Forward, Girl" by Melba Pattillo Beals

Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023