The word 心猿意马 is formed by directly combining two metaphorical constructs: 心猿, which pairs 心 (heart) with 猿 (monkey) to depict a restless heart, and 意马, which pairs 意 (mind) with 马 (horse) to depict a wandering mind. These four characters are joined in sequence to create a fixed idiom that conveys a state of distraction or unsettled thoughts.