Nonplus

Part of speech: noun (n.)

A state or condition which daffles reason or confounds judgment; insuperable difficalty; inability to proceed or decide; puzzle; quandary. Both of them are a perfect nonplus and baffle to all human understanding. South.

Part of speech: verb (v.)

To puzzle; to confound; to perplex; to cause to stop by embarrassment. He has been nonplused by Mr. Dry's desiring him to tell what it was that he endeavored to prove. Spectator.