A former country home, alternatively part of Turkey (4,5)
I believe the answer is:
asia minor
'part of turkey' is the definition.
(I've seen this before)
'a former country home alternatively' is the wordplay.
'former country' becomes 'Siam' (former name of Thailand).
'home' becomes 'in' (to be in is to be (at) home).
'alternatively' becomes 'or'.
'a'+'siam'+'in'+'or'='ASIA MINOR'
(Other definitions for asia minor that I've seen before include "several?" , "Historical name for Anatolia" , "part of Turkey" , "was visited by early missionary" , "Alternative name for Anatolia" .)