Cranium damaged by electronic nail treatment (8)
I believe the answer is:
manicure
'nail treatment' is the definition.
(I've seen this before)
'cranium damaged by electronic' is the wordplay.
'damaged' indicates anagramming the letters.
'by' is a charade indicator (letters next to each other).
'electronic' becomes 'e' (as in e-mail or e-books).
'cranium' is an anagram of 'manicur'.
'manicur'+'e'='MANICURE'
(Other definitions for manicure that I've seen before include "Care of hands and fingernails" , "Care of hands and nails" , "Cosmetic treatment for the hands" , "attention to extremities" , "Work on nails" .)