"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.
"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.
"cheap music hall or theater; place of amusement for the lowest classes," 1812, British slang, earlier "a fair" (1753), of unknown origin.