gullible [E19th] A gullible person was originally someone who could be ‘gulled’, or deceived. Gull in this sense is now rare, but was a very common word from the 16th to the 19th centuries, and was used by Shakespeare. It may have come from gull, an old dialect term for an unfledged bird, which had nothing to do with gull as in seagull: this was a medieval word that probably came from a Celtic language such as Welsh or Cornish.