the deep

WordReference Random House Learner's Dictionary of American English © 2025

deep /dip/   adj. and adv., -er, -est, n. 
adj. 

1. extending far down from the top or surface:
   a deep well.
2. extending far in or back from the front:
   a deep shelf.
3. extending far in width;
   broad:
   a deep border.
4. [after a noun indicating measurement] having a certain specified dimension or amount in depth:
   a tank 10 feet deep.
5. [~ + in] immersed or submerged:
   The road was deep in snow.
6. [before a noun] coming from far down:
   Now, take a deep breath.
7. made with the body bent or lowered to a considerable degree:
   a deep curtsy.
8. difficult to understand;
   abstruse;
   
   a book too deep for young children.
9. not superficial;
   serious;
   profound:
   deep thoughts.
10. [before a noun] sincere;
    intense;
    great:
    deep affections.
11. [before a noun] sound and heavy;
    undisturbed:
    deep sleep.
12. strong, dark, and vivid in color:
    a deep red.
13. low in pitch, such as sound:
    a deep, rich voice.
14. mysterious;
    hidden:
    deep secrets.
15. [ ~ + in] involved to a great extent:
    to be deep in debt.
16. giving one's full attention;
    absorbed;
    engrossed:
    [be + ~ + in] He was deep in thought.

adv. 

17. to or at a considerable or great depth:
    We were about ten feet deep when our ears popped.
18. [after a number, noun, or adjective indicating measurement] to a depth or breadth of (the number, noun, or adjective mentioned):
    The fans were lined up three deep around the block.
19. far on in time;
    late:
    They worked deep into the night.
20. within;
    far down:
    I still feel love for her deep in my heart.

n. [uncountable]

21. [ often: the + ~ + of] the midpoint or the part of greatest intensity:
    the deep of winter; in the deep of the night.
22. the deep, [Literary.] the sea or ocean:
    The deep was the drowned sailor's final resting place.

Idioms

23. Idioms go off the deep end:
    • to become emotionally overwrought:
      She went off the deep end when she was turned down for promotion.
    • to act without enough thought of the consequences:
      The committee went off the deep end with the Christmas decorations.
24. Idioms in deep, involved:
    He was in too deep with her and had to break off their relationship.
25. Idioms in deep water, in serious trouble:
    The company is in deep water and can barely make ends meet.

deep•ly, adv. 
deep•ness, n. [uncountable]

WordReference Random House Unabridged Dictionary of American English © 2025

deep  (dēp), adj. -er, -est, n., adv., -er, -est. 
adj. 

1. extending far down from the top or surface:
   a deep well; a deep valley.
2. extending far in or back from the front or from an edge, surface, opening, etc., considered as the front:
   a deep shelf.
3. extending far in width;
   broad:
   deep lace; a deep border.
4. ranging far from the earth and sun:
   a deep space probe.
5. having a specified dimension in depth:
   a tank 8 feet deep.
6. covered or immersed to a specified depth (often used in combination):
   standing knee-deep in water.
7. having a specified width or number of items from front to back (often used in combination):
   shelves that are 10 inches deep; cars lined up at the entrance gates three-deep.
8. extending or cutting far down relative to the surface of a given object:
   The knife made a deep scar in the table.
9. situated far down, in, or back:
   deep below the surface; deep in the woods.
10. reaching or advancing far down:
    a deep dive.
11. coming from far down:
    a deep breath.
12. made with the body bent or lowered to a considerable degree:
    a deep bow.
13. immersed or submerged in or heavily covered with (fol. by in):
    a road deep in mud.
14. difficult to penetrate or understand;
    abstruse:
    a deep allegory.
15. not superficial;
    profound:
    deep thoughts.
16. grave or serious:
    deep disgrace.
17. heartfelt;
    sincere:
    deep affections.
18. absorbing;
    engrossing:
    deep study.
19. great in measure;
    intense;
    extreme:
    deep sorrow.
20. sound and heavy;
    profound:
    deep sleep.
21. (of colors) dark and vivid:
    a deep red.
22. low in pitch, as sound, a voice, or the like:
    deep, sonorous tones.
23. having penetrating intellectual powers:
    a deep scholar.
24. profoundly cunning or artful:
    a deep and crafty scheme.
25. mysterious;
    obscure:
    deep, dark secrets.
26. immersed or involved;
    enveloped:
    a man deep in debt.
27. absorbed;
    engrossed:
    deep in thought.
28. Sport [Baseball.] relatively far from home plate:
    He hit the ball into deep center field.
29. Linguistics belonging to an early stage in the transformational derivation of a sentence;
    belonging to the deep structure.
30. Idioms go off the deep end:
    • to enter upon a course of action with heedless or irresponsible indifference to consequences.
    • to become emotionally overwrought.
31. Idioms in deep water:
    • in difficult or serious circumstances;
      in trouble.
    • 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.

n. 

32. Geology, Oceanography the deep part of a body of water, esp. an area of the ocean floor having a depth greater than 18,000 ft. (5400 m).
33. a vast extent, as of space or time.
34. the part of greatest intensity, as of winter.
35. Nautical, Naval Terms any of the unmarked levels, one fathom apart, on a deep-sea lead line. Cf. mark¹ (def. 20).
36. the deep, [Chiefly Literary.] the sea or ocean:
    He was laid to rest in the deep.

adv. 

37. to or at a considerable or specified depth:
    The boat rode deep in the water.
38. far on in time:
    He claimed he could see deep into the future.
39. profoundly;
    intensely.
40. Sport [Baseball.] at or to a deep place or position:
    The outfielders played deep, knowing the batter's reputation as a slugger.
41. Idioms in deep:
    • inextricably involved.
    • having made or committed oneself to make a large financial investment.

• bef. 900; Middle English dep, Old English dēop; akin to Gothic diups, Old Norse djupr, Old High German tiof 

deep′ness, n. 
Synonyms

• 14. recondite, mysterious, obscure, profound.
• 23. sagacious, wise, profound, shrewd.

Antonyms

• 1, 10.
• 15. –17, 23. shallow.

Collins Concise English Dictionary © HarperCollins Publishers::

deep / diːp/ adjective

1. extending or situated relatively far down from a surface: a deep pool
2. extending or situated relatively far inwards, backwards, or sideways
3. relatively far from the pitch: the deep field, deep square leg
4. (postpositive) of a specified dimension downwards, inwards, or backwards: six feet deep
5. coming from or penetrating to a great depth
6. difficult to understand or penetrate; abstruse
7. learned or intellectually demanding: a deep discussion
8. of great intensity; extreme: deep happiness, deep trouble
9. (postpositive) followed by in: absorbed or enveloped (by); engrossed or immersed (in): deep in study, deep in debt
10. very cunning or crafty; devious
11. mysterious or obscure: a deep secret
12. (of a colour) having an intense or dark hue
13. low in pitch or tone: a deep voice
14. go off the deep end ⇒ to lose one's temper; react angrily
15. to act rashly
16. in deep water ⇒ in a tricky position or in trouble
17. throw someone in at the deep end ⇒
    See end128

noun

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

adverb

1. far on in time; late: they worked deep into the night
2. profoundly or intensely
3. deep down ⇒ in reality, esp as opposed to appearance

Etymology: Old English dēop; related to Old High German tiof deep, Old Norse djupr

ˈdeeply adverb

ˈdeepness noun