Simon Templar sat around at home (5)
I believe the answer is:
saint
'simon templar' is the definition.
(I know that simon templar can be written as Saint)
'sat around at home' is the wordplay.
'around' indicates putting letters inside.
'at home' becomes 'in' ('I'm in' can mean 'I'm at home').
'sat' enclosing 'in' is 'SAINT'.
(Other definitions for saint that I've seen before include "Beatified person" , "Canonised person" , "eg Paul, Peter, Valentine" , "eg Pancras" , "Holy person" .)