The word "老奸巨猾" is formed by combining two parallel phrases: "老奸" and "巨猾". In this construction, "老" and "巨" act as intensifiers, meaning "very" or "extremely", while "奸" denotes "crafty" and "猾" means "sly". Thus, the idiom literally signifies "extremely crafty and extremely sly", resulting in a compound that emphasizes a high degree of deceitfulness through the amplification of these negative characteristics.