'Clearly'

It is better to be clear than to write 'Clearly, ____________.'

Similarly with 'surely,' 'plainly,' 'obviously,' 'undoubtedly,' and others.

What should we call such words?  Asseveratives?  Assuratives? 

I know a guy who, if you preface a remark with 'surely,' you receive in response, "Don't call me 'Shirley.'"