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deep (dēp)
adj. deep·er, deep·est
a. Extending far downward below a surface: a deep hole in the river ice.
b. Extending far inward from an outer surface: a deep cut.
c. Extending far backward from front to rear: a deep walk-in refrigerator.
d. Extending far from side to side from a center: a deep yard surrounding the house.
e. Far distant down or in: deep in the woods.
f. Coming from or penetrating to a depth: a deep sigh.
g. Sports Located or taking place near the outer boundaries of the area of play: deep left field.
2. Extending a specific distance in a given direction: snow four feet deep.
3. Far distant in time or space: deep in the past.
a. Difficult to penetrate or understand; recondite: a deep metaphysical theory.
b. Of a mysterious or obscure nature: a deep secret; ancient and deep tribal rites.
c. Very learned or intellectual; wise: a deep philosopher.
d. Exhibiting great cunning or craft: deep political machinations.
a. Of a grave or extreme nature: deep trouble; deepest deceit.
b. Very absorbed or involved: deep in thought; deep in financial difficulties.
c. Profound in quality or feeling: a deep trance; deep devotion.
6. Rich and intense in shade. Used of a color: a deep red.
7. Low in pitch; resonant: a deep voice.
8. Covered or surrounded to a designated degree. Often used in combination: waist-deep in the water; ankle-deep in snow.
9. Large in quantity or size; big: deep cuts in the budget.
10. Sports Having a sufficient number of capable reserve players: That team is not very deep.
1. To a great depth; deeply: dig deep; feelings that run deep.
2. Well along in time; late: worked deep into the night.
3. Sports Close to the outer boundaries of the area of play: played deep for the first three innings; ran deep into their opponents' territory.
1. often deeps
a. A deep place in land or in a body of water: drowned in the deep of the river.
b. A vast, immeasurable extent: the deep of outer space.
2. The extent of encompassing time or space; firmament.
3. The most intense or extreme part: the deep of night.
4. The ocean.
5. Nautical A sounding that falls between marks on a lead line and thus corresponds to an estimated depth rather than a precise depth.
deep down
At bottom; basically: Deep down, she was still a rebel.
in deep water
In difficulty.

[Middle English dep, from Old English dēop; see dheub- in the Appendix of Indo-European roots.]

deeply adv.
deepness n.

The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2022 by HarperCollins Publishers. All rights reserved.

Indo-European & Semitic Roots Appendices

    Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:

    Indo-European Roots

    Semitic Roots

    The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.