Queen showing restraint entertaining head of government, American (6)
I believe the answer is:
regina
'queen' is the definition.
(Latin for 'queen')
'restraint entertaining head of government american' is the wordplay.
'restraint' becomes 'rein' (I've seen this in another clue).
'entertaining' indicates putting letters inside.
'head of' indicates taking the first letters.
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
The first letter of 'government' is 'g'.
'rein' enclosing 'g' is 'regin'.
'regin'+'a'='REGINA'
'showing' acts as a link.
(Other definitions for regina that I've seen before include "monarch" , "Queen in legal issues" , "in Canada" , "Reigning queen's title" , "Queen (in law cases)" .)