Somewhat is an adverb. You can also use 'a little' instead which is more common. For example: The food is somewhat expensive The food is a little expensive

Don't be confused by this, however. There is a difference between "somewhat" and "a little". In my experience, "somewhat" is the stronger of the two, but, like I said, the difference is very subtle.

Somewhat is like saying a little/a bit, I am somewhat tired. His attitude made me somewhat angry. I would say there is no difference between somewhat and a little/a bit and I would use them interchangeably.