Sentence:  So shall we haue the people of our side, / Which for his fathers sake leane to the king, / But cannot brooke a night growne <WSD>mushrump</WSD>, / Such a one as my Lord of Cornewall is [...] 
Meaning of the word marked with <WSD> tags:  Upstart, a person who has quickly and undeservedly gained their position, power or wealth.