Presumed Hypatia has set a toughie, starting earlier (8)
I believe the answer is:
putative
'presumed' is the definition.
(thesaurus)
'hypatia has set a toughie starting earlier' is the wordplay.
I cannot really understand how this works, but
'set' could be 'put' (synonyms) and 'put' is located in the answer.
'a' is present in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for putative that I've seen before include "Supposed - tie up vat (anag)" , "Supposed or thought to be" , "Supposed, generally considered such" , "Supposed or reputed" , "Generally considered or reputed to be" .)