Cheese — French, originally — in legal case (5)
I believe the answer is:
brief
'legal case' is the definition.
(I've seen this before)
'cheese french originally' is the wordplay.
'cheese' becomes 'brie' (Brie is an example).
'originally' suggests taking the first letters.
The first letter of 'french' is 'f'.
'brie'+'f'='BRIEF'
'in' acts as a link.
(Other definitions for brief that I've seen before include "scanty" , "Document stating the facts of a legal case" , "Terse" , "Prime" , "Brusque - lawyer (slang)" .)