One lessening impact, or adding shine? (6)
I believe the answer is:
buffer
'one lessening impact' is the definition.
(a buffer lessens the impact of something)
'adding shine?' is the wordplay.
I cannot quite see how this works, but
'shine?' could be 'buff' (buffing is a kind of shining) and 'buff' is present in the answer.
The remaining letters 'er' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
'or' is the link.
(Other definitions for buffer that I've seen before include "Neutral area created to reduce conflict" , "Shock-preventing railway apparatus" , "Something that lessens the effect of an impact" , "doddery old man" , "It lessons the force of an impact, something in between" .)