Delivery includes organ (5)
I believe the answer is:
liver
'organ' is the definition.
(I know that liver is a type of internal organ)
'delivery includes' is the wordplay.
'includes' indicates a hidden word.
'LIVER' is hidden in the letters of 'delivery'.
(Other definitions for liver that I've seen before include "Organ; reddish-brown" , "Glandular organ of the stomach" , "Bile-secreting organ" , "Internal organ" , "Large gland" .)