Rocky hill in America is shaped like a doughnut (5)
I believe the answer is:
torus
'doughnut' is the definition.
(I've seen this before)
'rocky hill in america' is the wordplay.
'rocky hill' becomes 'tor' (I've seen this before).
'in america' becomes 'U.S.' ('US' is part of 'america').
'tor'+'us'='TORUS'
'is shaped like a' acts as a link.
This may not be correct. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for torus that I've seen before include "Ring-shaped object" , "Ring shape" , "Shape of doughnut" , "Architectural moulding" , "Doughnut-shaped solid" .)