Etymology
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cavern (n.)

"large, natural cave under the earth," late 14c., from Old French caverne (12c.) "cave, vault, cellar," from Late Latin caverna "cave," from Latin cavus "hollow" (from PIE root *keue- "to swell," also "vault, hole"). In Old English such a land feature might be called an eorðscræf.

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cavernous (adj.)

c. 1400, "full of caverns," from Latin cavernosus "full of cavities" (source also of Italian cavernoso, French caverneux), from caverna (see cavern). Meaning "full of cavities, porous" is from 1590s. Meaning "deely hollowed out" is recorded from 1830.

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*keue- 
*keuə-, Proto-Indo-European root meaning "to swell," also "vault, hole."

It forms all or part of: accumulate; accumulation; cave; cavern; cavity; coeliac; church; codeine; coelacanth; coeliac; coelomate; concave; cumulate; cumulative; cumulus; enceinte; excavate; kirk; kymatology; Kyrie eleison.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit svayati "swells up, is strong;" Greek kyein "to swell," koilos "hollow, hollowed out, spacious, deep;" Latin cumulus "a heap, pile, mass, surplus;" Lithuanian šaunas "firm, solid, fit, capable;" Middle Irish cua "hollow;" Armenian soyl "cavity."
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spelunk (n.)
"a cave, cavern, a vault," c. 1300, from Old French spelonque (13c.) or directly from Latin spelunca "a cave, cavern, grotto," from Greek spelynx (accusative spelynga, genitive spelyngos) "a cave, cavern," from spelos "a cave." An adjective, speluncar "of a cave" is recorded from 1855.
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grotto (n.)
"picturesque cavern or cave," 1610s, from Italian grotta, earlier cropta, a corruption of Latin crypta "vault, cavern," from Greek krypte "hidden place" (see crypt). Terminal -o may be from its being spelled that way in many translations of Dante's "Divine Comedy."
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hollowness (n.)
late 14c., "cave, cavern; internal empty space;" mid-15c., "condition of being hollow," from hollow (adj.) + -ness.
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spelunker (n.)
"a cave bug; one who explores caves as a hobby," 1942, agent noun formed from obsolete spelunk "cave, cavern." The verb spelunk "explore caves" and the verbal noun spelunking are attested from 1946 and appear to be back-formations.
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crypt (n.)

early 15c., cripte, "grotto, cavern," from Latin crypta "vault, cavern," from Greek krypte "a vault, crypt" (short for krypte kamara "hidden vault"), fem. of kryptos "hidden," verbal adjective from kryptein "to hide," which is of uncertain origin. Comparison has been made to Old Church Slavonic kryjo, kryti "to hide," Lithuanian kráuti "to pile up." Beekes writes that krypto "is formally and semantically reminiscent of [kalypto]; the verbs may have influenced each other." For this, see calypto-. But he adds, "However, since there is no good IE etymology, the word could be Pre-Greek." Meaning "underground burial vault or chapel in a church" is attested by 1789.

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peak (n.)

1520s, "pointed top, projecting summit," a variant of pike (n.4) "sharp point." Meaning "top of a mountain, a precipitous mountain with a more or less conical summit" is recorded by 1630s, though pike was used in this sense c. 1400. Figurative sense is 1784. Of beards, 1590s; of hats, 1650s. Meaning "point formed by hair on the forehead" is from 1833. As "the highest point" in any varying quantity, or the time when this occurs, by 1902. 

The Peak, the prominent hill in Derbyshire, England, is older than the word for "mountaintop;" compare Old English Peaclond, for the district, Pecsaetan, for the people who settled there, Peaces ærs for Peak Cavern. In this case it is sometimes said to be a reference to an elf-denizen Peac "Puck."

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character (n.)
Origin and meaning of character

mid-14c., carecter, "symbol marked or branded on the body;" mid-15c., "symbol or drawing used in sorcery;" late 15c., "alphabetic letter, graphic symbol standing for a sound or syllable;" from Old French caratere "feature, character" (13c., Modern French caractère), from Latin character, from Greek kharaktēr "engraved mark," also "symbol or imprint on the soul," properly "instrument for marking," from kharassein "to engrave," from kharax "pointed stake," a word of uncertain etymology which Beekes considers "most probably Pre-Greek."  The Latin ch- spelling was restored from 1500s.

The meaning of Greek kharaktēr was extended in Hellenistic times by metaphor to "a defining quality, individual feature." In English, the meaning "sum of qualities that define a person or thing and distinguish it from another" is from 1640s. That of "moral qualities assigned to a person by repute" is from 1712.

You remember Eponina, who kept her husband alive in an underground cavern so devotedly and heroically? The force of character she showed in keeping up his spirits would have been used to hide a lover from her husband if they had been living quietly in Rome. Strong characters need strong nourishment. [Stendhal "de l'Amour," 1822] 

Sense of "person in a play or novel" is first attested 1660s, in reference to the "defining qualities" he or she is given by the author. Meaning "a person" in the abstract is from 1749; especially "eccentric person" (1773). Colloquial sense of "chap, fellow" is from 1931. Character-actor, one who specializes in characters with marked peculiarities, is attested from 1861; character-assassination is from 1888; character-building (n.) from 1886.

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