Part you see in Hero and Leander’s union? (4)
I believe the answer is:
role
'part' is the definition.
(eg a theatrical role)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for role that I've seen before include "Playing part" , "Function in life" , "Duty" , "Part (in drama)" , "A part of lore" .)