Some part of crab is questionable for soup (6)
I believe the answer is:
bisque
'soup' is the definition.
(bisque is a kind of soup)
'some part of crab is questionable' is the wordplay.
'some part of' indicates the answer is hidden within the clue.
'BISQUE' is hidden in the letters of 'crab is questionable'.
'for' is the link.
(Other definitions for bisque that I've seen before include "Rich soup as made from lobster" , "Creamy soup" , "Shellfish soup - kind of pottery" , "Rich soup made from shellfish" , "Rich soup made from lobsters" .)