Etymology
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gall (n.1)

"bile, liver secretion," Old English galla (Anglian), gealla (West Saxon) "gall, bile," from Proto-Germanic *gallon "bile" (source also of Old Norse gall "gall, bile; sour drink," Old Saxon galle, Old High German galla, German Galle), from PIE root *ghel- (2) "to shine," with derivatives denoting "green, yellow," and thus "bile, gall." Informal sense of "impudence, boldness" first recorded American English 1882; but meaning "embittered spirit, rancor" is from c. 1200, from the old medicine theory of humors.

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gall (n.2)
"sore on skin caused by rubbing or chafing," Old English gealla "painful swelling, sore spot on a horse," probably from Latin galla "gall, lump on plant," originally "oak-gall" (see gall (n.3)). Perhaps from or influenced by gall (n.1) on notion of "poison-sore." Meaning "bare spot in a field" (1570s) is probably the same word. German galle, Dutch gal also are said to be from Latin.
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gall (v.)
"to make sore by chafing," mid-15c., from gall (n.2). Earlier "to have sores, be sore" (early 14c.). Figurative sense of "harass, vex, irritate, chafe the spirit of," is from 1570s. A past-participle adjective gealled is found in Old English, but OED says this is from the noun. Related: Galled; galling.
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gall (n.3)
"excrescence on a plant caused by the deposit of insect eggs," especially on an oak leaf, late 14c., from Latin galla "oak-gall," which is of uncertain origin. They were harvested for use in medicines, inks, dyes.
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ox-gall (n.)

"bitter fluid secreted by the liver of an ox, used in paints and coloring," 1630s, from ox + gall (n.1).

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galling (adj.)
"irritating, offensive, extremely annoying," 1580s, figurative use of present participle of gall (v.).
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*ghel- (2)

Proto-Indo-European root meaning "to shine;" it forms words for "gold" (the "bright" metal), words denoting colors, especially "yellow" and "green," also "bile, gall," for its color, and a large group of Germanic gl- words having to do with shining and glittering and, perhaps, sliding. Buck says the interchange of words for yellow and green is "perhaps because they were applied to vegetation like grass, cereals, etc., which changed from green to yellow."

It forms all or part of: arsenic; Chloe; chloral; chloride; chlorinate; chlorine; chloro-; chloroform; chlorophyll; chloroplast; cholecyst; choler; cholera; choleric; cholesterol; cholinergic; Cloris; gall (n.1) "bile, liver secretion;" gild; glad; glance; glare; glass; glaze; glazier; gleam; glee; glib; glide; glimmer; glimpse; glint; glissade; glisten; glister; glitch; glitter; glitzy; gloaming; gloat; gloss (n.1) "glistening smoothness, luster;" glow; glower; gold; guilder; jaundice; melancholic; melancholy; yellow; zloty.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit harih "yellow, tawny yellow," hiranyam "gold;" Avestan zari "yellow;" Old Persian daraniya-, Avestan zaranya- "gold;"  Greek khlōros "greenish-yellow color,"  kholos "bile, gall, wrath;"  Latin helvus "yellowish, bay," Gallo-Latin gilvus "light bay;" Lithuanian geltonas "yellow;" Old Church Slavonic zlutu, Polish żółty, Russian zeltyj "yellow;" Latin galbus "greenish-yellow," fellis "bile, gall;" Lithuanian žalias "green," želvas "greenish," tulžis "bile;" Old Church Slavonic zelenu, Polish zielony, Russian zelenyj "green;" Old Irish glass, Welsh and Breton glas "green," also "gray, blue;" Old English galla "gall, bile," geolu, geolwe, German gelb, Old Norse gulr "yellow;" Old Church Slavonic zlato, Russian zoloto, Old English gold, Gothic gulþ "gold;" Old English glæs "glass; a glass vessel."

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cholecystitis (n.)

"inflammation of the gall bladder," 1846, from cholecyst "gall bladder" + -itis "inflammation."

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