Like chestnut-mounted thug in fairy tale (3,6,4)
I believe the answer is:
red riding hood
'fairy tale' is the definition.
Both the definition and answer are singular nouns.
Maybe you can see a link between them that I can't see?
'like chestnut-mounted thug' is the wordplay.
'like chestnut' becomes 'red' (chestnut is a shade of red. I am not sure about the 'like' bit.).
'mounted' becomes 'riding' (both can mean on a horse).
'thug' becomes 'hood' (synonyms).
'red'+'riding'+'hood'='RED RIDING HOOD'
'in' is the link.
Can you help me to learn more?
(Other definitions for red riding hood that I've seen before include "Fairy tale character involved with a wolf" , "Girl in tale encountering wolf" , "Little fairytale character in a cloak" .)