Its use can be seen on reflection (6)
I believe the answer is:
mirror
'reflection' is the definition.
(thesaurus)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for mirror that I've seen before include "copy of > tabloid" , "Reflecting glass" , "newspaper" , "in which driver glances back" , "Alice went through one (Carroll)" .)