Talk a blue streak? (4)
I believe the answer is:
cuss
'talk a blue streak?' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for cuss that I've seen before include "Stubborn person" , "Swear (slang)" , "Use bad language (informal)" , "Blaspheme" , "Oath; (annoying sort of) person" .)