One member permitted? That's understood (8)
I believe the answer is:
implicit
'understood' is the definition.
(similar in meaning)
'one member permitted?' is the wordplay.
'one' becomes 'i' (Roman numeral).
'member' becomes 'MP' (Member of Parliament).
'permitted?' becomes 'licit' (licit means allowed or permitted).
'i'+'mp'+'licit'='IMPLICIT'
'that's' is the link.
(Other definitions for implicit that I've seen before include "Implicit" , "unreserved" , "Inherent but not made clear" , "Taken for granted" , "Understood but not openly stated" .)