Greek god — part herald, part messenger (6)
I believe the answer is:
hermes
This could be a double definition.
'greek god' is the first definition.
(Hermes is an example)
'messenger' is the second definition.
(Greek messenger god)
'part herald part' is the link.
This may not be right. Some or all of it may belong to one of the definitions.
Can you help me to learn more?
(Other definitions for hermes that I've seen before include "Greek messenger of the gods, like Roman Mercury" , "Greek messenger god" , "Winged messenger" , "Greek god of commerce and theft" , "Messenger and herald of the gods" .)