Climbed hill to pen note (7)
I believe the answer is:
mounted
'climbed' is the definition.
('mount' can be a synonym of 'climb')
'hill to pen note' is the wordplay.
'hill' becomes 'mound' (mound is a kind of hill).
'to pen' means one lot of letters goes inside another.
'note' becomes 'te' (**).
'mound' going around 'te' is 'MOUNTED'.
(Other definitions for mounted that I've seen before include "Rose" , "On a steed" , "Riding a horse" , "On horseback" , "riding horses" .)