The idiom 恨之入骨 is formed by combining 恨, meaning "to hate", with 之, a classical Chinese pronoun acting as the object of the hatred, followed by 入, meaning "to enter", and 骨, meaning "bone". The construction places the verb-object phrase 恨之 before the complementary phrase 入骨, which literally describes the hatred entering the bones, thereby using a metaphorical resultative structure to express that the hatred is so intense it penetrates to the marrow.