Sherwood hero to mug one knight (5)
I believe the answer is:
robin
'sherwood hero' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'mug one knight' is the wordplay.
'mug' becomes 'rob' (to mug someone is to rob them).
'one' becomes 'i' (Roman numeral).
'knight' becomes 'n' (chess abbreviation).
'rob'+'i'+'n'='ROBIN'
'to' is the link.
Can you help me to learn more?
(Other definitions for robin that I've seen before include ". . . . . Hood was a medieval outlaw" , "Small brown thrush" , "flier" , "Famous outlaw" , "Garden bird" .)