The definition for diffident is "Lacking self–confidence." Used in a sentence: The diffident student never raised her hand in class, even when she knew the answer.

The definition for mandate is "An official order or commission to do something." Used in a sentence: Martha reluctantly obeyed the mandate to vacate her apartment.

The definition for negate is "To make invalid." Used in a sentence: Paula negated Tiffany's argument by proving that her main premise was false.

The definition for periodic is "Occurring at regular intervals." Used in a sentence: The periodic innterruptions of the cuckoo clock prevented Li from concentrating.

The definition for raucous is "Noisy, rowdy." Used in a sentence: Serena, who preferred quiet conversation, left the rancous party.