Gleam noticed around top of hill (5)
I believe the answer is:
sheen
'gleam' is the definition.
(thesaurus)
'noticed around top of hill' is the wordplay.
'noticed' becomes 'seen' (I've seen this before).
'around' indicates putting letters inside.
'top of' suggests taking the first letters.
The initial letter of 'hill' is 'h'.
'seen' enclosing 'h' is 'SHEEN'.
(Other definitions for sheen that I've seen before include "Surface gloss" , "Surface shine" , "brilliance" , "Polish" , "Superficial brightness" .)