◎家贼难防jiāzéi-nánfáng
[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] 家属或内部的人作弊营私难以防范
⒈ 家庭内部的贼人或内奸最难防范。
引《五灯会元·同安志禅师法嗣·梁山缘观禅师》：“问：‘家贼难防时如何？’师曰：‘识得不为寃。’”
清李渔《凰求凤·悟奸》：“这等看起来，真箇是家贼难防，连星相医卜的话都是他教导的了？”
比喻内部的敌人或坏人最难防范。