Organ of an active kind, with a key part (6)
I believe the answer is:
kidney
'organ' is the definition.
(kidney is a kind of organ)
'an active kind with a key part' is the wordplay.
'an active' indicates anagramming the letters (the letters are active/moving).
'with' means one lot of letters go next to another.
'a key part' becomes 'ey' (I can't explain this - if you can you should believe this answer much more).
'kind' anagrammed gives 'kidn'.
'kidn'+'ey'='KIDNEY'
'of' is the link.
Can you help me to learn more?
(Other definitions for kidney that I've seen before include "class" , "Bean-shaped organ" , "Character" , "Bodily organ" , "body part" .)