The word "天啊" is formed by combining the character "天", meaning "heaven" or "sky", with the character "啊", a modal particle used to express strong emotion. Together, they create an interjection where "天" serves as the subject of exclamation, often invoking a celestial reference for emphasis, and "啊" adds an audible, emotional tone, resulting in a phrase equivalent to "Oh my God!" or "Heavens!" in English.