Great joy in breaking toenail (7)
I believe the answer is:
elation
'great joy' is the definition.
(I've seen this before)
'breaking toenail' is the wordplay.
'breaking' indicates anagramming the letters.
'toenail' anagrammed gives 'ELATION'.
'in' is the link.
(Other definitions for elation that I've seen before include "Toenail (anag) -- delight" , "Feeling of intense delight" , "Delight, thrill" , "There's great joy" , "Great happiness and exhilaration" .)