Euclid's study (8)
I believe the answer is:
geometry
'euclid's study' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for geometry that I've seen before include "Mathematics of points, lines, curves and surfaces" , "Euclid's science" , "Mathematics of points, lines etc." , "school subject" , "branch of mathrmatics" .)