Fish, Cornish cheese, and eggs rejected (8)
I believe the answer is:
stingray
'fish' is the definition.
(stingray is a kind of fish)
'cornish cheese and eggs rejected' is the wordplay.
'cornish cheese' becomes 'gray' (I can't justify this - if you can you should give a lot more credence to this answer).
'and' says to put letters next to each other (I've seen this in other clues).
'eggs' becomes 'nits' (nit is a kind of egg).
'rejected' says the letters should be written in reverse.
'nits' backwards is 'stin'.
'gray' put after 'stin' is 'STINGRAY'.
Can you help me to learn more?
(Other definitions for stingray that I've seen before include "Poisonous spined fish" , "Large venomous fish -- it's angry (anag)" , "Marine creature with venomous tail" , "menace in the water" , "Dangerous fish" .)