adjective, deep·er, deep·est.


adverb, deep·er, deep·est.


    go off the deep end,
    1. to enter upon a course of action with heedless or irresponsible indifference to consequences.
    2. to become emotionally overwrought.
    in deep,
    1. inextricably involved.
    2. having made or committed oneself to make a large financial investment.
    in deep water,
    1. in difficult or serious circumstances; in trouble.
    2. in a situation beyond the range of one's capability or skill: You're a good student, but you'll be in deep water in medical school.

Origin of deep

before 900; Middle English dep, Old English dēop; akin to Gothic diups, Old Norse djupr, Old High German tiof
Related formsdeep·ness, nounnon·deep, adjectiveo·ver·deep, adjectiveun·deep, adjectiveun·deep·ly, adverb

Synonyms for deep

Antonyms for deep

1, 10, 15–17, 23. shallow. Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

British Dictionary definitions for undeep



extending or situated relatively far down from a surfacea deep pool
extending or situated relatively far inwards, backwards, or sidewaysa deep border of trees
cricket relatively far from the pitchthe deep field; deep third man
  1. (postpositive)of a specified dimension downwards, inwards, or backwardssix feet deep
  2. (in combination)a six-foot-deep trench
coming from or penetrating to a great deptha deep breath
difficult to understand or penetrate; abstruse
learned or intellectually demandinga deep discussion
of great intensity; extremedeep happiness; deep trouble
(postpositive foll by in) absorbed or enveloped (by); engrossed or immersed (in)deep in study; deep in debt
very cunning or crafty; deviousa deep plot
mysterious or obscurea deep secret
(of a colour) having an intense or dark hue
low in pitch or tonea deep voice
go off the deep end informal
  1. to lose one's temper; react angrily
  2. mainly USto act rashly
in deep water in a tricky position or in trouble
throw someone in at the deep end See end 1 (def. 28)


any deep place on land or under water, esp below 6000 metres (3000 fathoms)
the deep
  1. a poetic term for the ocean
  2. cricketthe area of the field relatively far from the pitch
the most profound, intense, or central partthe deep of winter
a vast extent, as of space or time
nautical one of the intervals on a sounding lead, one fathom apart


far on in time; latethey worked deep into the night
profoundly or intensely
deep down informal in reality, esp as opposed to appearanceshe is a very kind person deep down
deep in the past long ago
Derived Formsdeeply, adverbdeepness, noun

Word Origin for deep

Old English dēop; related to Old High German tiof deep, Old Norse djupr
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for undeep



Old English deop "deep water," especially the sea, from the source of deep (adj.).



Old English deop "profound, awful, mysterious; serious, solemn; deepness, depth," deope (adv.), from Proto-Germanic *deupaz (cf. Old Saxon diop, Old Frisian diap, Dutch diep, Old High German tiof, German tief, Old Norse djupr, Danish dyb, Swedish djup, Gothic diups "deep"), from PIE *dheub- "deep, hollow" (cf. Lithuanian dubus "deep, hollow, Old Church Slavonic duno "bottom, foundation," Welsh dwfn "deep," Old Irish domun "world," via sense development from "bottom" to "foundation" to "earth" to "world").

Figurative senses were in Old English; extended 16c. to color, sound. Deep pocket "wealth" is from 1951. To go off the deep end "lose control of oneself" is slang first recorded 1921, probably in reference to the deep end of a swimming pool, where a person on the surface can no longer touch bottom. When 3-D films seemed destined to be the next wave and the biggest thing to hit cinema since talkies, they were known as deepies (1953).

Online Etymology Dictionary, © 2010 Douglas Harper

Idioms and Phrases with undeep


In addition to the idioms beginning with deep

  • deep down
  • deep end
  • deep pocket
  • deep six
  • deep water

also see:

  • beauty is only skin deep
  • between a rock and a hard place (devil and deep blue sea)
  • go off the deep end
  • in deep
  • still waters run deep
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.