As found on Merriam-Webster Online Dictionary
You may use this tool freely
http://www.hometownlinks.com/study_a..._thesaurus.htm
One entry found for gullible.
Main Entry: gull·ible
Variant(s): also gull·able /'g&-l&-b&l/
Function: adjective
: easily duped or cheated
- gull·ibil·i·ty /"g&-l&-'bi-l&-tE/ noun
- gull·ibly /'g&-l&-blE/ adverb