—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. Baseball.relatively far from home plate: He hit the ball into deep center field. 29. Ling.belonging to an early stage in the transformational derivation of a sentence; belonging to the deep structure.
30. go off the deep end, a. to enter upon a course of action with heedless or irresponsible indifference to consequences.
b. to become emotionally overwrought.
31. in deep water, a. in difficult or serious circumstances; in trouble.
b. 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. 1. 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).
2. a vast extent, as of space or time.
3. the part of greatest intensity, as of winter.
4. Naut.any of the unmarked levels, one fathom apart, on a deep-sea lead line. Cf. mark1 (def. 20).
5. the deep,Chiefly Literary.the sea or ocean: He was laid to rest in the deep.
—adv. 1. to or at a considerable or specified depth: The boat rode deep in the water. 2. far on in time: He claimed he could see deep into the future. 3. profoundly; intensely.
4. Baseball.at or to a deep place or position: The outfielders played deep, knowing the batter's reputation as a slugger. 5. in deep, a. inextricably involved.
b. having made or committed oneself to make a large financial investment.