Guardian article on reflecting (5)
I believe the answer is:
angel
'guardian' is the definition.
(guardian angel)
'article on reflecting' is the wordplay.
'article' becomes 'an' (indefinite article).
'on' becomes 'leg' (cricket term, fielding positions).
'reflecting' says the letters should be written in reverse.
'leg' backwards is 'gel'.
'an'+'gel'='ANGEL'
(Other definitions for angel that I've seen before include "eg Gabriel" , "Winged messenger" , "somewhere in Islington" , "Ministering spirit" , "Holy being" .)