At a country home being entertained (8)
I believe the answer is:
astatine
'at' is the definition.
('astatine' can be a synonym of 'at')
'a country home being entertained' is the wordplay.
'country' becomes 'state' ('state' can be a synonym of 'country').
'home' becomes 'in' ('he's home' can mean 'he's in').
'being entertained' indicates putting letters inside.
'state' going around 'in' is 'statine'.
'a'+'statine'='ASTATINE'
(Other definitions for astatine that I've seen before include "Rare element" , "radioactive material" , "Atomic number 85" , "Radioactive element" , "Chemical element At" .)