in deep

Idioms  

1. 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 .

2. 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 .

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Example Sentences

Some microbial mats thrive in deep, dark environments by feeding on chemical energy rather than sunlight.

From Science Daily • Apr. 3, 2026

A significant proportion of Hungary's estimated 800,000 Roma minority live in deep poverty.

From BBC • Mar. 26, 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

Shortly before his job was eliminated, Bryant openly spoke out against the cuts in The Washington Post and Boston Globe, which he said landed him in deep trouble at the Pentagon.

From Salon • Mar. 11, 2026

I breathed in deep and forced my Jell-O legs onto the stage.

From "Sir Fig Newton and the Science of Persistence" by Sonja Thomas