gudgeon (n.1) Look up gudgeon at
European small freshwater fish, early 15c., from Middle French goujon, from Old French gojon (14c.), from Latin gobionem (nominative gobio), alteration of gobius, from Greek kobios, a kind of fish, a word of unknown origin. They are easily caught, hence the figurative sense of "a credulous person" (one who will "bite" at "bait"), from 1580s.
gudgeon (n.2) Look up gudgeon at
"pivot on the end of a beam," c. 1400, from Old French gojon "pin, peg, spike" (13c.), perhaps somehow an altered sense of gudgeon (n.1).