deep / dēp/ • adj. 1. extending far down from the top or surface: a deep gorge the lake was deep and cold. ∎  extending or situated far in or down from the outer edge or surface: deep in the woods. ∎  (after a measurement and in questions) extending a specified distance from the top, surface, or outer edge: the well was 200 feet deep. ∎  [in comb.] as far up or down as a specified point: standing waist-deep in the river. ∎  in a specified number of ranks one behind another: [in comb.] standing three-deep at the bar. ∎  taking in or giving out a lot of air: she took a deep breath. ∎  Baseball far back in the outfield: his first pitch was hit into deep left field.2. very intense or extreme: a deep sleep. ∎  (of an emotion or feeling) intensely felt: deep disappointment. ∎  profound or penetrating in awareness or understanding: a deep analysis. ∎  difficult to understand: this is all getting too deep for me. ∎  (deep in) fully absorbed or involved in (a state or activity): they were deep in their own thoughts. ∎  (of a person) unpredictable and secretive: that Thomas is a deep one.3. (of sound) low in pitch and full in tone; not shrill.4. (of color) dark and intense.• n. (the deep) poetic/lit. the sea: denizens of the deep. ∎  (usu. deeps) a deep part of the sea: the dark and menacing deeps. ∎  (usu. deeps) fig. a remote and mysterious region: the deeps of her imagination.• adv. far down or in; deeply: traveling deep into the countryside | fig. his passion runs deep. ∎  (in sports) distant from the start of a play or the forward line of one's team: the defense played deep.PHRASES: the deep end the end of a swimming pool where the water is deepest.go off the deep end inf. give way immediately to an emotional outburst, esp. of anger. ∎  go mad; behave extremely strangely: they looked at me as if I had gone off the deep end.in deep inf. inextricably involved in or committed to a situation.in deep water inf. in trouble or difficulty.jump (or be thrown) in at the deep end inf. face a difficult problem or undertaking with little experience of it.DERIVATIVES: deep·ness n.

deep deep-six destroy or dispose of (something) irretrievably, perhaps from the custom of burial at sea at a depth of six fathoms.
Deep South the south-eastern region of the US regarded as embodying traditional Southern culture and traditions.
Deep Throat codename (from the title of a pornographic film, 1972) given in the Watergate affair to the journalists' principal anonymous informant; from this, deep throat is used to mean a person working for an organization who anonymously supplies information on misconduct to an outside source. The original Deep Throat has never been publicly identified.

See also beauty is only skin deep, still waters run deep.

deep having great extension downwards; fig. profound OE.; penetrating XIII; (of colour) intense; subtle, crafty XVI. OE. dēop = OS. diop, diap (Du. diep), OHG. tiuf (G. tief), ON. djúpr, Goth. diups :- Gmc. *deupaz, f. *deup- *dup- (see DIP). As sb. deep water OE.; the deep the ocean (XIV).
Hence deepen XVI, deeply XV; see -EN 5, -LY 2.

DEEP Directly Elected European Parliament