Ancient Greek mathematician (6)
'ancient greek mathematician' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for euclid that I've seen before include "Greek mathematician, d. mid-3rd century BC" , "Ancient Greek mathematician" , "Geometrician of the 3rd century BC" , "Greek mathematician c. three hundred BC" , "Alexandrian mathematician" .)
(Other definitions for archimedes that I've seen before include "Greek mathematician ('Eureka')" , "Ancient Greek scientist (of buoyancy principle)" , "'Eureka' scientist" , "Ancient Greek mathematician/inventor" , "Greek physicist" .)