Webster's Revised Unabridged Dictionary · 1913

Deep

Deep (dēp) , adjective

[Old English dep, deop, Anglo-Saxon deóp; akin to Dutch diep, German tief, Icelandic djūpr, Swedish diup, Danish dyb, Gothic diups; from the root of English dip, dive. See Dip, Dive.]

1.
Extending far below the surface; of great perpendicular dimension (measured from the surface downward, and distinguished from high, which is measured upward); far to the bottom; having a certain depth; as, a deep sea.
The water where the brook is deep. — Shakespeare
2.
Extending far back from the front or outer part; of great horizontal dimension (measured backward from the front or nearer part, mouth, etc.); as, a deep cave or recess or wound; a gallery ten seats deep; a company of soldiers six files deep.
Shadowing squadrons deep. — Milton
Safely in harbor Is the king's ship in the deep nook. — Shakespeare
3.
Low in situation; lying far below the general surface; as, a deep valley.
4.
Hard to penetrate or comprehend; profound; -- opposed to shallow or superficial; intricate; mysterious; not obvious; obscure; as, a deep subject or plot.
Speculations high or deep. — Milton
A question deep almost as the mystery of life. — De Quincey
O Lord,... thy thoughts are very deep. — Bible (KJV) - Psalm xcii. 5
5.
Of penetrating or far-reaching intellect; not superficial; thoroughly skilled; sagacious; cunning.
Deep clerks she dumbs. — Shakespeare
6.
Profound; thorough; complete; unmixed; intense; heavy; heartfelt; as, deep distress; deep melancholy; deep horror.
Deep despair. — Milton
Deep silence. — Milton
Deep sleep. — Gen. ii. 21
Deeper darkness. — Hoole
Their deep poverty. — 2 Cor. viii. 2
An attitude of deep respect. — Motley
7.
Strongly colored; dark; intense; not light or thin; as, deep blue or crimson.
8.
Of low tone; full-toned; not high or sharp; grave; heavy.
The deep thunder. — Byron
The bass of heaven's deep organ. — Milton
9.
Muddy; boggy; sandy; -- said of roads. — Chaucer
The ways in that vale were very deep. — Clarendon
Collocations (2)
A deep line of operations (Military) , a long line.
Deep mourning (Costume) , mourning complete and strongly marked, the garments being not only all black, but also composed of lusterless materials and of such fashion as is identified with mourning garments.

Deep , adverb

To a great depth; with depth; far down; profoundly; deeply.
Deep-versed in books, and shallow in himself. — Milton
Drink deep, or taste not the Pierian spring. — Pope

Deep, in its usual adverbial senses, is often prefixed to an adjective; as, deep-chested, deep-cut, deep-seated, deep-toned, deep-voiced, “deep-uddered kine.”

Deep , noun

1.
That which is deep, especially deep water, as the sea or ocean; an abyss; a great depth.
Courage from the deeps of knowledge springs. — Cowley
The hollow deep of hell resounded. — Milton
Blue Neptune storms, the bellowing deeps resound. — Pope
2.
That which is profound, not easily fathomed, or incomprehensible; a moral or spiritual depth or abyss.
Thy judgments are a great deep. — Bible (KJV) - Psalm xxxvi. 6
The deep of night is crept upon our talk. — Shakespeare
Collocations (1)
Deep of night , the most quiet or profound part of night; dead of night.