Internal organ (6)
'internal organ' is the definition.
(I know that stomach is a type of internal organ)
This is all the clue.
(Other definitions for stomach that I've seen before include "Put up with" , "Mac hosts his organ" , "Inside" , "Endure; organ" , "Digestive organ" .)
(Other definitions for spleen that I've seen before include "Organ of the body and short temper" , "Abdominal organ - bad temper" , "Internal organ; spite" , "Organ supposedly controlling temper" , "The organ once thought to be the seat of anger" .)