Mumpish is an adjective that means Sullen or sulky. 

The origin of our word of the day isn’t clear, but we know the word mump has been with us since the 16th century, with the adjective mumpish emerging in the 17th century. Here’s an example of it use:

Carl’s mumpish demeanour probably harmed his political career. After all, who wants to vote for somebody who seems moody and sullen all the time.