Aim to have day in American hills (7)
I believe the answer is:
uplands
'hills' is the definition.
(I've seen this before)
'aim to have day in american' is the wordplay.
'aim' becomes 'plan' (I've seen this before).
'to have' means one lot of letters go next to another.
'day' becomes 'd' (abbreviation for day).
'in' is an insertion indicator.
'american' becomes 'us' (abbreviation for United States).
'plan'+'d'='pland'
'pland' placed into 'us' is 'UPLANDS'.
(Other definitions for uplands that I've seen before include "High region" , "Regions of high ground" , "hills" , "hilly country" .)