He can see a new aspect to the hill (9)
I believe the answer is:
spectator
'he can' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'a new aspect to the hill' is the wordplay.
'a new' indicates an anagram.
'to the hill' becomes 'tor' (tor is a kind of hill).
'aspect' is an anagram of 'specta'.
'specta'+'tor'='SPECTATOR'
'see' acts as a link.
Can you help me to learn more?
(Other definitions for spectator that I've seen before include "Periodical" , "Looker-on" , "given weekly inspection?" , "One attends match" , "One watching a game" .)