Ultimately ruining dinner, fibre and cartilage (7)
I believe the answer is:
gristle
'cartilage' is the definition.
(synonyms)
'ultimately ruining dinner fibre' is the wordplay.
'ultimately' suggests the final letters.
'fibre' becomes 'istle' (I've seen this before).
The last letters of 'ruining dinner' are 'gr'.
'gr'+'istle'='GRISTLE'
'and' is the link.
(Other definitions for gristle that I've seen before include "It's hard to eat" , "Stir leg (anag.)" , "Glister (anag)" , "Chewy cartilage" , "Sinew" .)