Etymology
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deep six (n.)

"place where something is discarded," by 1921 (in phrase give (something) the deep six), originally in motorboating slang, perhaps from earlier underworld noun sense of "the grave" (1929), which is perhaps a reference to the usual grave depth of six feet. But the phrase (in common with mark twain) also figured in sailing jargon, of sounding, for a measure of six fathoms:

As the water deepened under her keel the boyish voice rang out from the chains: "By the mark five—and a quarter less six—by the deep six—and a half seven—by the deep eight—and a quarter eight." ["Learning the Road to Sea," in Outing magazine, February 1918]

In general use by 1940s. As a verb from 1953.

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deep-freeze (n.)
registered trademark (U.S. Patent Office, 1941) of a type of refrigerator; used generically for "cold storage" since 1949.
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Donald 

surname, from 13c. Scottish Dofnald, Dufenald, probably from Gaelic Domhnall, Old Irish Domnall (pronounced "Dovnall"), from Proto-Celtic *Dubno-valos "world-mighty, ruler of the world," from *walos "ruler" (from PIE root *wal- "to be strong") + Old Irish domun "world," from PIE root *dheub- "deep, hollow," via sense development from "bottom" to "foundation" to "earth" to "world" (see deep (adj.)). A top 10 name for boys born in the U.S. between 1923 and 1943. Disney's Donald Duck cartoon character debuted in 1934.

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profound (adj.)

c. 1300, "characterized by intellectual depth, very learned," from Old French profont, profund (12c., Modern French profond) and directly from Latin profundus "deep, bottomless, vast," also "obscure; profound; immoderate," from pro "forth" (from PIE root *per- (1) "forward") + fundus "bottom" (see fund (n.)).

The literal and figurative senses both were in Latin, but English, having already deep, has employed this word primarily in its figurative sense; however in 15c. it was used of deep lakes or wounds. Sense of "deeply felt, intense" is from c. 1400. Related: Profoundly. A verb profound "to penetrate, reach inside, saturate, fill" is attested in English from 15c.-17c.

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dip (v.)

Old English dyppan "to plunge or immerse temporarily in water, to baptize by immersion," from Proto-Germanic *daupejanan (source also of Old Norse deypa "to dip," Danish døbe "to baptize," Old Frisian depa, Dutch dopen, German taufen, Gothic daupjan "to baptize"), related to Old English diepan "immerse, dip," and probably a causative of Proto-Germanic *deup- "deep" (see deep (adj.)).

Intransitive sense of "plunge into water or other liquid" and transferred sense "to sink or drop down a short way" are from late 14c. From c. 1600 as "to raise or take up by a dipping action;" from 1660s as "to incline downward;" from 1776 as "to lower and raise (a flag, etc.) as if by immersing."

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depth (n.)

late 14c., "a deep place, deep water, the sea," also "distance or extension from the top down (opposed to height) or from without inward," apparently formed in Middle English on model of long/length, broad/breadth; from dēp "deep" (see deep (adj.)) + -th (2). Replaced older deopnes "deepness." Though the word is not recorded in Old English, the formation was in Proto-Germanic, *deupitho-, and corresponds to Old Saxon diupitha, Dutch diepte, Old Norse dypð, Gothic diupiþa.

From c. 1400 as "the part of anything most remote from the boundary or outer limit." From 1520s as "quality of extending a considerable distance downward or inward." Figurative use in reference to thought, ideas, etc., "profoundness," from 1580s.

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dive (v.)

c. 1200, diven, "descend or plunge headfirst into water," from a merger of Old English dufan "to dive, duck, sink" (intransitive, class II strong verb; past tense deaf, past participle dofen) and dyfan "to dip, submerge" (weak, transitive), from Proto-Germanic verb *dubijan, from PIE *dheub- "deep, hollow" (see deep (adj.)).

In the merger of verbs the weak forms predominated and the strong inflections were obsolete by 1300. The past tense remained dived into 19c., but in that century dove emerged, perhaps on analogy of drive/drove. The change began to be noted in the late 1850s by Canadian and U.S. editors: Bartlett (1859) notes it as an Americanism, "Very common among seamen and not confined to them," and a paper read before the Canadian Institute in 1857 reports it in Canadian English. All note its use by Longfellow in "Hiawatha" (1855).

From early 13c. as "to make a plunge" in any way; of submarines by 1872; of airplanes by 1908 (hence dive-bombing, dive-bomber, both 1931). Figurative sense of "plunge entirely into something that engrosses the attention" is from 1580s. In Middle English also transitive, "to submerge (something), make to sink down."

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baritone (n.)

c. 1600, "male voice between tenor and bass," from Italian baritono, from Greek barytonos "deep-toned, deep-sounding," from barys "heavy, deep," also, of sound, "strong, deep, bass" (from PIE root *gwere- (1) "heavy") + tonos "tone," from PIE root *ten- "to stretch."

Technically, "ranging from lower A in bass clef to lower F in treble clef." Meaning "singer having a baritone voice" is from 1821. As a type of brass band instrument, it is attested from 1949. As an adjective, 1729 in reference to the voice, 1854 of musical instruments (originally the concertina).

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bathukolpian (adj.)
also bathycolpian, etc., "big-breasted," 1825, from Greek bathykolpos "with full breasts," literally "deep-bosomed," from bathys "deep" (see benthos) + kolpos "breast" (see gulf (n.)). With -ian.
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taedium vitae 
Latin, "weariness of life; a deep disgust with life tempting one to suicide."
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