Part of Myanmar, in a terrain that’s steep (8)
I believe the answer is:
marinate
'steep' is the definition.
(marinating is a kind of steeping)
'part of myanmar in a terrain' is the wordplay.
'part of' indicates a hidden word.
'MARINATE' is hidden in the letters of 'myanmar in a terrain'.
'that's' is the link.
(Other definitions for marinate that I've seen before include "Steep before cooking" , "Soak food in a minaret" , "Rain team (anag.)" , "Soak or steep meat or fish" , "steep in liquor" .)