Legendary creature’s heart mostly filled with gold (7)
I believe the answer is:
centaur
'legendary creature's' is the definition.
The answer and definition can be both people as well as being singular nouns.
I also know that 'legendary' relates to this answer.
'heart mostly filled with gold' is the wordplay.
I cannot really see how this works, but
'gold' could be 'au' (Au is the chemical symbol for gold) and 'au' is present in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for centaur that I've seen before include "Mythological creature" , "Mythic man-horse" , "Mythical hybrid" , "Mythical semi-equine beast" , "Mythological man-horse" .)