Cloak bishop covered in fish eggs (4)
I believe the answer is:
robe
'cloak' is the definition.
(thesaurus)
'bishop covered in fish eggs' is the wordplay.
'bishop' becomes 'B' (chess abbreviation).
'covered in' indicates putting letters inside.
'fish eggs' becomes 'roe' (synonyms).
'b' going within 'roe' is 'ROBE'.
(Other definitions for robe that I've seen before include "Formal attire" , "Gown or dress of office" , "Any loose flowing garment" , "Old cloak for Boer" , "Formal vestment" .)