n.

1. the central and most intense or profound part
   
   • in the deep of night
   • in the deep of winter
2. a long steep-sided depression in the ocean floor;
   trench, oceanic abyss
3. literary term for an ocean
   
   • denizens of the deep

adj.

1. relatively deep or strong; affecting one deeply
   
   • a deep breath
   • a deep sigh
   • deep concentration
   • deep emotion
   • a deep trance
   • in a deep sleep
2. marked by depth of thinking
   
   • deep thoughts
   • a deep allegory
3. having great spatial extension or penetration downward or inward from an outer surface or backward or laterally or outward from a center; sometimes used in combination
   
   • a deep well
   • a deep dive
   • deep water
   • a deep casserole
   • a deep gash
   • deep massage
   • deep pressure receptors in muscles
   • deep shelves
   • a deep closet
   • surrounded by a deep yard
   • hit the ball to deep center field
   • in deep space
   • waist-deep
4. very distant in time or space
   
   • deep in the past
   • deep in enemy territory
   • deep in the woods
   • a deep space probe
5. extreme
   
   • in deep trouble
   • deep happiness
6. having or denoting a low vocal or instrumental range;
   bass
   
   • a deep voice
   • a bass voice is lower than a baritone voice
   • a bass clarinet
7. strong; intense;
   rich
   
   • deep purple
   • a rich red
8. relatively thick from top to bottom
   
   • deep carpets
   • deep snow
9. extending relatively far inward
   
   • a deep border
10. (of darkness) very intense;
    thick
    
    • thick night
    • thick darkness
    • a face in deep shadow
    • deep night
11. large in quantity or size
    
    • deep cuts in the budget
12. with head or back bent low
    
    • a deep bow
13. of an obscure nature;
    cryptic, cryptical, inscrutable, mysterious, mystifying
    
    • the new insurance policy is written without cryptic or mysterious terms
    • a deep dark secret
    • the inscrutable workings of Providence
    • in its mysterious past it encompasses all the dim origins of life"- Rachel Carson; "rituals totally mystifying to visitors from other lands
14. difficult to penetrate; incomprehensible to one of ordinary understanding or knowledge;
    abstruse, recondite
    
    • the professor's lectures were so abstruse that students tended to avoid them
    • a deep metaphysical theory
    • some recondite problem in historiography
15. exhibiting great cunning usually with secrecy
    
    • deep political machinations
    • a deep plot

adv.

1. to a great depth;
   deeply
   
   • dived deeply
   • dug deep
2. to an advanced time;
   late
   
   • deep into the night
   • talked late into the evening
3. to far into space; "penetrated deep into enemy territory"; "went deep into the woods";