Numpty is an informal British noun used to describe a foolish or stupid person. While it is not necessarily a derogatory term, it is still better to have alternative synonyms to describe such people without hurting their sentiments. Some of the common synonyms for numpty include idiot, fool, dunce, nincompoop, dolt, blockhead, dimwit, twit, and clown. Other alternatives could be buffoon, bonehead, ignoramus, or knucklehead. These words can come handy while communicating with such people without being too harsh and disrespectful. Regardless of the word used, it is always advisable to be respectful and polite in our language and communication.