Vegetable gourd (6)
I believe the answer is:
marrow
'vegetable gourd' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for marrow that I've seen before include "Soft bone tissue" , "Large gourd fruit or stuff in bone cavities" , "Connective tissue in bones" , "Oversized courgette" , "Large vegetable gourd or stuff in bones" .)