Giant with a hundred eyes (5)
I believe the answer is:
argus
'giant with a hundred eyes' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for argus that I've seen before include "Legendary Guardian" , "Monster with many eyes slain by Hermes in Greek myth" , "Giant with one hundred eyes in Greek mythology" , "Alert watchman" , "Various brown butterflies" .)