Etymology
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abyss (n.)
Origin and meaning of abyss
late 14c. in Latin form abyssus, "depths of the earth or sea; primordial chaos;" early 14c. as abime "depths of the earth or sea; bottomless pit, Hell" (from Old French; see abysm). Both are from Late Latin abyssus "bottomless pit," from Greek abyssos (limne) "bottomless (pool)," from abyssos "bottomless, unfathomed," hence, generally, "enormous, unfathomable," also as a noun, he abyssos "the great depth, the underworld, the bottomless pit." This is a compound of a- "without" (see a- (3)) + byssos "bottom," a word of uncertain origin possibly related to bathos "depth" [Liddell & Scott]. Watkins suggests a connection with the root of bottom (n.); Beekes suggests it is pre-Greek.

The current form in English is a 16c. partial re-Latinization. Greek abyssos was used in Septuagint to translate Hebrew tehom "original chaos" and was used in the New Testament for "Hell." OED notes, "the word has had five variants, abime, abysm, abysmus, abyssus, abyss; of which abyss remains as the ordinary form, and abysm as archaic or poetic." In reference to a seemingly bottomless gulf from 1630s.
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abyssal (adj.)
1690s, "unfathomable, unsearchably deep, like an abyss," from abyss + -al (1). Since 19c. mainly "inhabiting or belonging to the depths of the ocean" (used especially of the zone of ocean water below 300 fathoms), though in 19c. abysmal was more common in oceanography.
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abysm (n.)
Origin and meaning of abysm
"bottomless gulf, greatest depths," c. 1300, from Old French abisme "chasm, abyss, depths of ocean, Hell" (12c., Modern French abîme), from Vulgar Latin *abyssimus (source also of Spanish and Portuguese abismo), which represents perhaps a superlative of Latin abyssus or a formation on analogy of Greek-derived words in -ismus; see abyss. It survived only as a poetic variant of abyss; as late as early 17c. it was pronounced to rhyme with time.
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Tartarus (n.)
in Homer and older Greek mythology, the sunless abyss below Hades, from Greek Tartaros, of uncertain origin; "prob. a word of imitative origin, suggestive of something frightful" [Klein]. Later in Greek almost synonymous with Hades.
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abysmal (adj.)
1650s, "pertaining to an abyss," formed in English from abysm + -al (1). Perhaps only a dictionary word before 19c. Weakened sense of "extremely bad" is first recorded 1904, perhaps from abysmal ignorance (suggestive of its "depth"), an expression attested from 1847. Related: Abysmally.
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archipelago (n.)
c. 1500, from Italian arcipelago "the Aegean Sea" (13c.), from arci- "chief, principal," from Latin archi- (see arch-) + pelago "pool; gulf, abyss," from Medieval Latin pelagus "pool; gulf, abyss, sea," from Greek pelagos "sea, high sea, open sea, main" (see pelagic).

The elements of the word are Greek, but there is no record of arkhipelagos in ancient or Medieval Greek (the modern word in Greek is borrowed from Italian), so the word perhaps is an Italian compound or an alteration in Italian of Medieval Latin Egeopelagus, from Greek Aigaion pelagos "Aegean Sea." The Aegean being full of island chains, the meaning was extended in Italian to "any sea studded with islands" (a sense attested in English from c. 1600) and to the islands themselves. Related: Archipelagian; archipelagic.
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regurgitation (n.)

c. 1600, "act of pouring or rushing back," chiefly medical (of blood, digestive fluid, etc.), from Medieval Latin regurgitationem (nominative regurgitatio), noun of action from past-participle stem of regurgitare "to overflow," from re- "back" (see re-) + Late Latin gurgitare "engulf, flood" (found in Latin ingurgitare "to pour in"), from gurges "whirlpool, gorge, abyss" (see gurges).

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swallow (n.2)
"an act of swallowing," 1822, from swallow (v.). In late Old English and Middle English it meant "gulf, abyss, hole in the earth, whirlpool," also, in Middle English, "throat, gullet." Compare Old Norse svelgr "whirlpool," literally "devourer, swallower." Meaning "as much as one can swallow at once, mouthful" is from 1861.
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groin (n.)
"oblique depression of the body between the abdomen and thighs," 1590s, earlier grine (1530s), from Middle English grynde "groin" (c. 1400), originally "depression in the ground," from Old English grynde "abyss," perhaps also "depression, hollow," from Proto-Germanic *grundus (see ground (n.)). Altered 16c. by influence of loin or obsolete groin "snout of a pig." The architectural groin "curving edge formed by the intersection of two vaults" is from 1725.
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Abyssinia (n.)
old name for Ethiopia, 1630s, from Modern Latin Abyssinia, from Arabic Habasah, the name for the region, said to be from Amharic hbsh "mixed" or Arabic habash "mixture," in reference to the different races dwelling there. In 1920s-30s popular as a slang pun for the parting salutation "I'll be seeing you." Related: Abyssinian (1620s; as a breed of domestic cat, 1876). In early use also Abyssine.
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