Heads of firms often hold sway overseas (7)
I believe the answer is:
foreign
'overseas' is the definition.
(similar in meaning)
'heads of firms often hold sway' is the wordplay.
'heads of' indicates taking the first letters.
'hold sway' becomes 'reign' (I've seen this before).
The initial letters of 'firms often' is 'fo'.
'fo'+'reign'='FOREIGN'
(Other definitions for foreign that I've seen before include "Peculiar" , "not typical" , "Extraneous" , "not appropriate" , "Unfamiliar; from abroad" .)