African male in perfect health ingests arsenic (5)
I believe the answer is:
Here is my best explanation:
'african' is the definition.
(I've seen this before)
I don't understand how the remainder of the clue works.
(Other definitions for masai that I've seen before include "Member of an African pastoral people", "An African", "East African tribesman", "East African pastoralist", "Ma is a member of an African people", "Pastoral African people", "Pastoral people of East Africa - as I am (anag)", "Well-known tribe of Eastern Africa", "Highlander in Africa" and "A language".)