The word 忧虑 is formed by combining the characters 忧 and 虑, each contributing to the meaning of worry. 忧 is a phono-semantic character composed of the heart radical 忄, indicating emotion, and the phonetic component 尤. 虑 is also phono-semantic, historically derived from elements like 虍 and 思, representing thought or concern. Together, they form a compound where both characters share similar semantic meanings related to anxiety.