As a guardian he was fabulous (5)
I believe the answer is:
argus
'as a guardian he was fabulous' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'he was fabulous' is the wordplay.
I cannot really see how this works, but
'he' could be 'gus' and 'gus' is located in the answer.
The remaining letters 'ar' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for argus that I've seen before include "Type of butterfly" , "Monster with many eyes slain by Hermes in Greek myth" , "Various brown butterflies" , "In Greek myth, a many-eyed monster slain by Hermes" , "Greek giant with 100 eyes" .)