Relatives' extraordinary earnings (8)
I believe the answer is:
grannies
'relatives'' is the definition.
(grannie is a kind of relative)
'extraordinary earnings' is the wordplay.
'extraordinary' indicates an anagram.
'earnings' anagrammed gives 'GRANNIES'.
(Other definitions for grannies that I've seen before include "Earnings for old ladies" , "Earnings for elderly ladies" , "older relations" , "Nans" .)