Tell you it's a very gentle incline (7)
I believe the answer is:
apprise
'tell' is the definition.
(I've seen this before)
'it's a very gentle incline' is the wordplay.
'it's a very gentle' becomes 'app' (I can't justify this - if you can you should believe this answer much more).
'incline' becomes 'rise' (rise is a kind of incline).
'app'+'rise'='APPRISE'
'you' acts as a link.
Can you help me to learn more?
(Other definitions for apprise that I've seen before include "tip off" , "Tell, advise" , "Inform, make aware of" , "Give notice" , "Inform, make known to" .)