1、家贼难防的解释是：家贼难防jiāzéi-nánfáng。(1)家属或内部的人作弊营私难以防范。家贼难防[jiāzéinánfáng]⒈家属或内部的人作弊营私难以防范。英thiefinthefamilyisdifficulttodetect;athieffromwithinishardtoguardagainst;itisdifficulttoforestallathiefwithinthehouse。