Hid a horse around part of America (5)
I believe the answer is:
idaho
'part of america' is the definition.
(I know that Idaho is part of United States of America)
'hid a horse around' is the wordplay.
'around' indicates a hidden word.
'IDAHO' can be found hidden inside 'hid a horse'.
(Other definitions for idaho that I've seen before include "Northern US state" , "State of north-west USA" , "The Gem State (US)" , "43rd US state" , "State of NW US" .)