To be a wet blanket makes little difference to Damien! (6)
I believe the answer is:
dampen
'to be' is the definition.
Although both the answer and definition are verbs in their base form, I don't see how one could define the other.
'a wet blanket makes little difference to damien' is the wordplay.
I cannot really see how this works, but
'a' could be 'amp' (A is the symbol for the amp or ampere) and 'amp' is located in the answer.
The remaining letters 'den' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for dampen that I've seen before include "get a bit wet" , "Discourage in moist manner" , "Make moist or depressed" , "Make moist or depress spirits" , "Stifle" .)