Simple song about an aromatic plant (7)
I believe the answer is:
dittany
'aromatic plant' is the definition.
(I've seen this before)
'simple song about an' is the wordplay.
'simple song' becomes 'ditty' (ditty can mean a basic song).
'about' is an insertion indicator.
'ditty' enclosing 'an' is 'DITTANY'.
(Other definitions for dittany that I've seen before include "Aromatic plant" , "oil-producer" , "Shrub" .)