Something for breakfast? It’s nice, really — in part (6)
I believe the answer is:
cereal
'something for breakfast?' is the definition.
(cereal is often eaten for breakfast)
'nice really in part' is the wordplay.
'in part' says the answer is hidden in the clue.
'CEREAL' is hidden in the letters of 'nice really'.
'it's' is the link.
(Other definitions for cereal that I've seen before include "Contents of breakfast bowl" , "Eg, wheat, rye, corn" , "Something for brekkie" , "Breakfast food made from grain" , "Maize, rye or the like" .)