Etymology
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gaffe (n.)

"blunder," 1909, perhaps from French gaffe "clumsy remark," originally "boat hook" (15c.), from Old Provençal gafar "to seize," probably from a Germanic source, from Proto-Germanic *gaf-, which is perhaps from PIE root *kap- "to grasp." Sense connection between the hook and the blunder is obscure; the gaff was used to land big fish. Or the Modern English word might derive from British slang verb gaff "to cheat, trick" (1893); or gaff "criticism" (1896), from Scottish dialect sense of "loud, rude talk" (see gaff (n.2)).

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gaff (n.1)
"iron hook," c. 1300, gaffe, from Old French gaffe "boat hook" (see gaffe). Specifically of the hook on a fishing spear from 1650s. As a type of spar from 1769. Related: gaff-hook.
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gaff (n.2)
"talk," 1812, in phrase blow the gaff "spill a secret," of uncertain origin. OED points out Old English gafspræc "blasphemous or ribald speech," and Scottish gaff "loud, rude talk" (by 1825). Compare gaffe.
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goof (n.)

1916, "stupid person," American English, perhaps a variant of English dialect goff "foolish clown" (1869), from 16c. goffe, probably from French goffe "awkward, stupid," which is of uncertain origin. Or English goffe may be from Middle English goffen "speak in a frivolous manner," which is possibly from Old English gegaf "buffoonery," and gaffetung "scolding." Sense of "a blunder" is c. 1954, probably influenced by gaffe. Also compare goofer, goopher which appears in representations of African-American dialect from 1887 in the sense of "a curse, spell," probably from an African word.

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*kap- 

Proto-Indo-European root meaning "to grasp."

It forms all or part of: accept; anticipate; anticipation; behave; behoof; behoove; cable; cacciatore; caitiff; capable; capacious; capacity; capias; capiche; capstan; caption; captious; captivate; captive; captor; capture; case (n.2) "receptacle;" catch; catchpoll; cater; chase (n.1) "a hunt;" chase (v.) "to run after, hunt;" chasse; chasseur; conceive; cop (v.) "to seize, catch;" copper (n.2) "policeman;" deceive; emancipate; except; forceps; gaffe; haft; have; hawk (n.); heave; heavy; heft; incapacity; inception; incipient; intercept; intussusception; manciple; municipal; occupy; participation; perceive; precept; prince; purchase; receive; recipe; recover; recuperate; sashay; susceptible.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit kapati "two handfuls;" Greek kaptein "to swallow, gulp down," kope "oar, handle;" Latin capax "able to hold much, broad," capistrum "halter," capere "to grasp, lay hold; be large enough for; comprehend;" Lettish kampiu "seize;" Old Irish cacht "servant-girl," literally "captive;" Welsh caeth "captive, slave;" Gothic haban "have, hold;" Old English hæft "handle," habban "to have, hold."

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gaffer (n.)
1580s, "elderly rustic," apparently (based on continental analogies) a contraction of godfather (compare gammer). Originally a term of respect, also applied familiarly; from "old man" it was extended by 1841 to foremen and supervisors, which sense carried over in early 20c. to "electrician in charge of lighting on a film set."
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