Etymology
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bitterness (n.)
Old English biternys "bitterness, grief;" see bitter + -ness. Figurative sense (of feelings, etc.) is attested earlier than literal sense (of taste), which will surprise no one who reads any amount of Anglo-Saxon literature.
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rancor (n.)

c. 1200, rancour, "a nourished envy; bitterness, hatred, malice," from Old French rancor "bitterness, resentment; grief, affliction," from Late Latin rancorem (nominative rancor) "rancidness, a stinking smell" (Palladius); "grudge, bitterness" (Hieronymus and in Late Latin), from Latin rancere "to stink," a word of unknown etymology (compare rancid). Sometimes in 15c. medical works the word is used in English in its literal Latin sense.

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embitter (v.)

"make bitter," c. 1600, from em- (1) + bitter (adj.). Now rare in its literal sense; figurative meaning "affect with bitterness or unhappiness" is attested by 1630s. Related: Embittered; embitterment.

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poignance (n.)

1769, of words, expressions, etc., "point, sharpness, power of irritation;" see poignant + -ance. As "power of stimulating the organs of taste" by 1782; in reference to emotional states, "painfulness, bitterness" by 1812.

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exacerbate (v.)

"increase the bitterness or virulence of, make (a feeling, a conflict, etc.) more hostile or malignant," 1650s, a back-formation from exacerbation or else from Latin exacerbatus, past participle of exacerbare "irritate, provoke." Related: Exacerbated; exacerbating.

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heartburn (n.)
mid-13c., herte-brine "lust," later "burning sensation in the esophagus, indigestion" (mid-15c.); see heart (n.) + burn (n.). Compare cardiac for confusion of "heart" and "stomach." A Middle English alternative was herte-brenning "anger, bitterness" (c. 1400), also "heartburn" (mid-15c.).
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acrimony (n.)

1540s, "quality of being sharp or pungent in taste," from French acrimonie or directly from Latin acrimonia "sharpness, pungency of taste," figuratively "acrimony, severity, energy," abstract noun from acer "sharp" (fem. acris), from PIE root *ak- "be sharp, rise (out) to a point, pierce") + -monia suffix of action, state, condition. Figurative extension to personal sharpness or bitterness is by 1610s.

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bittersweet (adj.)
"uniting bitterness and sweetness," 1610s, from bitter (adj.) + sweet (adj.). Perhaps older, as the same word is used as a noun in Middle English (late 14c.) for drinks or experiences that are both bitter and sweet and especially in reference to a type of apple; later of woody nightshade (1560s). Greek had a similarly formed compound, glykypikros, literally "sweet-bitter."
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acerbity (n.)
Origin and meaning of acerbity

1570s, from French acerbité, from Latin acerbitatem (nominative acerbitas) "harshness, sharpness, bitterness, sourness," literal and figurative (as in virus acerbitatis "the poison of malice"), from acerbus "bitter to taste, sharp, sour, tart," from Proto-Italic *akro-po- "sharp" (from PIE root *ak- "be sharp, rise (out) to a point, pierce"). Earliest use in English is figurative, of "sharp and bitter" persons. Of tastes, from 1610s. Latin acerbus is related to acer "sharp" as superbus "haughty" to super "above."

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jaundice (n.)
"morbid condition characterized by yellowish skin and eyes (caused by bile pigments in the blood)," c. 1300, jaunis, from Old French jaunice, earlier jalnice, "yellowness" (12c.), from jaune/jalne "yellow," from Latin galbinus "greenish yellow" (also source of Italian giallo), extended form of galbus, which probably is from PIE root *ghel- (2) "to shine," with derivatives denoting "green" and "yellow." With unetymological -d- (compare sound (n.1)).

Figurative meaning "feeling in which views are colored or distorted" first recorded 1620s, from yellow's association with bitterness and envy (see yellow (adj.)). In Old English geolu adl "yellow sickness;" in Middle English also gulesought.
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