The word "炯炯" is formed by reduplicating the single character "炯". The character "炯" is constructed as a phonetic-semantic compound, combining the semantic component "火" (fire), which conveys the meaning of brightness or light, with the phonetic component "冋", which indicates its pronunciation. This duplication results in an adjective that intensifies the original meaning, specifically describing something as brightly shining, often applied to eyes.