Hid a horse round part of America (5)
I believe the answer is:
idaho
'america' is the definition.
The definition and answer can be both locations as well as being singular nouns.
Perhaps there's an association between them I don't understand?
'hid a horse round part' is the wordplay.
'part' indicates the answer is hidden within the clue.
'IDAHO' is hidden within 'hid a horse round'.
'of' acts as a link.
(Other definitions for idaho that I've seen before include "Northern US state" , "US state in the Rocky Mountains" , "silver-mining state" , "part of US near Washington" , "US state S. of Montana" .)