The word "惊叹" is formed by combining the character "惊", meaning to startle or be amazed, which itself is composed of the heart radical "忄" indicating emotion and the phonetic component "京" suggesting pronunciation, with the character "叹", meaning to sigh or exclaim, composed of the mouth radical "口" indicating vocalization and the component "又" contributing to its form. Together, these characters semantically merge to express the act of marveling or exclaiming in admiration, with each part directly contributing to the word's overall meaning.