It involves a big bill for fish (7)
I believe the answer is:
pelican
'bill for fish' is the definition.
The answer and definition can be both animals as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'it involves a big' is the wordplay.
I cannot quite understand how this works, but
'it' could be 'e' ('e' can mean 'electronic' which is similar to 'IT') and 'e' is located in the answer.
'a' could be 'an' and 'an' is present in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for pelican that I've seen before include "The large bird is in place" , "Large bird with pouch in bill for storing fish" , "Long-billed waterbird" , "In place (anag.)" , "Aquatic, billed bird" .)