Discontinued fish in to be stewed (8)
I believe the answer is:
obsolete
'discontinued' is the definition.
(I've seen this before)
'fish in to be stewed' is the wordplay.
'fish' becomes 'sole' (sole is a kind of fish).
'in' is an insertion indicator.
'stewed' is an anagram indicator.
'to'+'be'='tobe'
'tobe' anagrammed gives 'obte'.
'sole' placed inside 'obte' is 'OBSOLETE'.
(Other definitions for obsolete that I've seen before include "Gone out of use and no longer effective" , "Pass" , "Discontinued" , "Outmoded, passe" , "No longer current" .)