( saying ) if you already have or control sth, it is difficult for sb else to take it away from you, even if they have the legal right to it
POSSESSION IS NINE TENTHS OF THE LAW
Meaning of POSSESSION IS NINE TENTHS OF THE LAW in English
Oxford Advanced Learner's English Dictionary. Оксфордский английский словарь для изучающик язык на продвинутом уровне. 2005