The state of being unwilling or unable to believe something; a feeling of doubt or disbelief. From Latin incredulitās (unbelief, doubt), from incredulus (unbelieving, incredulous), from in- (not) + credulus (believing, trustful), from credere (to believe, to trust). The term 'incredulity' has been used in English since the 15th century to describe the state of being unwilling or unable to believe something. It is derived from the Latin word 'incredulitas', which means 'unbelief' or 'distrust'.