The word "窈窕" is formed from two phonosemantic characters, each constructed with the radical "穴" (cave) as a semantic component suggesting depth or enclosure. "窈" combines "穴" with the phonetic component "幼" (yǒu), which approximates pronunciation and implies delicacy, while "窕" combines "穴" with the phonetic component "兆" (zhào) for sound and a nuance of fineness. The compound arises from pairing these characters based on their shared radical and complementary phonetic elements.