African runner's wealthiest, having lost millions (7)
I believe the answer is:
ostrich
'african runner's' is the definition.
(I've seen this in another clue)
I don't understand how the remainder of the clue works.
(Other definitions for ostrich that I've seen before include "Fast winger" , "Runner" , "Someone unprepared to face the facts" , "one tries to hide in the sand" , "One refusing to face facts; flightless African bird" .)