Stammer (7)
I believe the answer is:
stutter
'stammer' is the definition.
(I know that stammer can be written as stutter)
This is all the clue.
(Other definitions for stutter that I've seen before include "Speech defect in repeating first consonants of words" , "Struggle with one's words" , "s...say?" , "Falter" , "Stumble over words" .)