Gullible means believing anything anybody tells you, however unlikely. Utterly gullible, a gullible audience, too gullible.
It is a criticism of judgement rather than of intelligence, and the joke about gullible not being in the dictionary works precisely because the word invites the trick it names. It attaches to victims of scams and of practical jokes. Note gullibility; credulous, which is the more formal synonym; and gull as an old verb meaning to deceive, which is probably where the word comes from.
1adjectivegullibleBelieving anything anybody says, however unlikely.
“Only a gullible person would believe that email asking for their bank details.”
gullible is a quality of credulity.
Also accepted in games: naive
The origin is uncertain — probably from gull, an old verb meaning to deceive, or from a word for an unfledged bird. Either way the image is of something easily taken.
Old Norse
gulr — yellow, pale
Middle English
gole
English, today
gullible
Built from
Origin unknown. Either from gull + ible; or alternatively from Middle English gole, goll, gol (“an unfledged bird, silly fellow”), perhaps from Old Norse gulr (“yellow, pale”), from the hue of its down.
Etymology from Wiktionary, CC BY-SA