家贼难防

◎家属或内部的人作弊营私难以防范。

英文thief in the family is difficult to detect; a thief from within is hard to guard against; it is difficult to forestall a thief within the house;

◎比喻内部的敌人或坏人最难防范。

例证《五灯会元 · 卷一四 · 同安志禅师法嗣》：“问：『家贼难防时如何？』师曰：『识得不为冤。』”