Song about knave, knight and rustic (8)
I believe the answer is:
arcadian
'rustic' is the definition.
('arcadian' can be a synonym of 'rustic')
'song about knave knight' is the wordplay.
'song' becomes 'aria' (aria is a kind of song).
'about' means one lot of letters goes inside another.
'knave' becomes 'cad' (I've seen this before).
'knight' becomes 'n' (chess).
'aria' placed around 'cad' is 'arcadia'.
'arcadia'+'n'='ARCADIAN'
'and' is the link.
(Other definitions for arcadian that I've seen before include "Can a raid take place in poetically rural kind of setting?" , "Of idealised country life" , "Country dweller" , "Green" .)