credulity

credibility means belief on proved evidences and credulity means believing too easily

CRED means to believe so, credo, credible, credence, credit, credential, credulity, incredulous, creed, incredible all are associated with believe.

If you gave your friend a fake credit card, and if he/she think's it's real then he's a credulous person.

Cred - Believe + lit = little == Believe with little evidence.

if money is credit in our account then we belive the bank