Etymology
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caustic (adj.)

c. 1400, "capable of burning or destroying organic tissue, corrosive," from Latin causticus "burning, caustic," from Greek kaustikos "capable of burning; corrosive," from kaustos "combustible; burnt," verbal adjective from kaiein, the Greek word for "to burn" (transitive and intransitive) in all periods, which is of uncertain origin with no certain cognates outside Greek.

Figurative sense of "sarcastic, severely critical" is attested from 1771. As a noun "a caustic substance," early 15c., from the adjective.

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hypocaust (n.)
"arched fire chamber for heating rooms above via pipes," 1670s, from Late Latin hypocaustum, from Greek hypokauston, literally "heated from below," from hypo- "under; up from under" (see hypo-) + kauston, verbal adjective of kaiein "to burn" (see caustic).
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encaustic 
c. 1600 (n.), "art of encaustic painting;" 1650s (adj.) "produced by burning in," from Greek enkaustikos, from enkaiein "to burn in" from en (see en- (2)) + kaiein "to burn" (see caustic). "Strictly applicable only to painting executed or finished by the agency of heat" [Century Dictionary].
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calm (adj.)
late 14c., of the sea, "windless, without motion or agitation;" of a wind, "light, gentle," perhaps via Old French calme "tranquility, quiet," or directly from Old Italian calma "quiet, fair weather," which probably is from Late Latin cauma "heat of the mid-day sun" (in Italy, a time when everything rests and is still), from Greek kauma "heat" (especially of the sun), from kaiein "to burn" (see caustic). Spelling influenced by Latin calere "to be hot." Figurative application to social or mental conditions, "free from agitation or passion," is from 1560s.
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holocaust (n.)
Origin and meaning of holocaust

mid-13c., "sacrifice by fire, burnt offering," from Old French holocauste (12c.), or directly from Late Latin holocaustum, from Greek holokauston "a thing wholly burnt," neuter of holokaustos "burned whole," from holos "whole" (from PIE root *sol- "whole, well-kept") + kaustos, verbal adjective of kaiein "to burn" (see caustic).

Originally a Bible word for "burnt offerings," given wider figurative sense of "massacre, destruction of a large number of persons" from 1670s. The Holocaust "Nazi genocide of European Jews in World War II," first recorded 1957, earlier known in Hebrew as Shoah "catastrophe." The word itself was used in English in reference to Hitler's Jewish policies from 1942, but not as a proper name for them.

English chronicler Richard of Devizes in his contemporary account of the coronation of Richard I in 1189 used the word holocaust when he described the mass murder of the Jews of London, although he meant it as "a sacrificial offering."

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ink (n.)

"the black liquor with which men write" [Johnson], mid-13c., from Old French enche, encre "dark writing fluid" (12c.), earlier enque (11c.), originally enca, from Late Latin encaustum, from Late Greek enkauston. This is the neuter of the past-participle adjective enkaustos "burned in," from the stem of enkaiein "to burn in," from en- "in" (see en- (1)) + kaiein "to burn" (see caustic).

In Pliny the word is the name of a kind of painting executed by fire or heat. Later it was the name of the purple-red ink, the sacrum encaustum, used by the Roman emperors to sign their documents; this was said to have been obtained from the ground remains of certain shellfish, formed into writing fluid by the application of fire or heat, which explained the name. In the Code of Justinian, the making of it for common uses, or by common persons, was prohibited under penalty of death and confiscation of goods.

It denoted a kind of painting practised by the ancients, in which the crayon was dipped in wax of various colours. Encausto pingere is to practise this art, paint in encaustic or enamel. Encaustum afterwards came to signify an ink for the purpose of writing; and the "sacred encaustum" of Justinian's Code was an ink which the Roman Emperors used for imperial subscriptions. It was of the imperial colour, reddish purple, and was made of the purple dye, prepared in some way by the application of fire. (So that in this use of the word, the notion of burning which there is in the etymology, is still retained.) [from footnote in "The Life, Letters, and Sermons of Bishop Herbert de Losinga," Oxford, 1878]

The usual words for "ink" in Latin was atramentum (source of Old French arrement), literally "anything that serves to dye black," from ater "black;" the Greek word was melan, neuter of melas "black." The Old English word for it was blæc, literally "black," and compare Swedish bläck, Danish blæk "ink." Spanish and Portuguese (tinta) and German (tinte) get their "ink" words from Latin tinctus "a dyeing."

Donkin credits a Greek pronunciation, with the accent at the front of the word, for the French evolution; the same Latin word, behaving regularly, became inchiostro (with unetymological -r-) in Italian, encausto in Spanish. As an adjective, inken (c. 1600) occasionally has been used. Ink-slinger, contemptuous for "journalist," is from 1870. The psychologist's ink-blot test attested from 1915.

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vitriolic (adj.)
1660s, from French vitriolique (16c.) or from vitriol + -ic. Figurative sense "biting, caustic, very severe" is by 1841.
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cautery (n.)

1540s, "heated metal used for burning or searing animal tissue," from Latin cauterium "branding iron," from Greek kauterion, from kauteriazein (see cauterize). From 1570s as "a burning or searing" (by a hot iron or caustic substance).

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quicklime (n.)

"caustic lime, lime not yet slaked with water," late 14c., from quick (adj.) "living" + lime (n.1). A loan-translation of Latin calx viva. So called perhaps for being unquenched, or for the vigorousness of its qualities; compare Old English cwicfyr "sulfur."

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mordacious (adj.)

"given to biting," 1640s (originally figurative, of words, speech, etc.), from Latin mordac-, stem of mordax "biting," from mordēre "to bite," which is perhaps from an extended form of PIE root *mer- "to rub away, harm." Middle English had mordicant (adj.) "corrosive, caustic" (in medicine), early 15c., also mordicative. Related: Mordacity (c. 1600).

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