The word 虚弱 is formed by combining two characters, each contributing a core idea to create a unified concept. The first character, 虚 (xū), conveys a sense of emptiness, hollowness, or lack of substantial strength, as in something insubstantial or depleted. The second character, 弱 (ruò), directly means weak, feeble, or fragile. When placed together, 虚 describes the internal, foundational condition, a void or deficiency of vitality, while 弱 describes the outward, observable manifestation of that condition. The formation is thus a logical and semantic fusion where one element (虚) explains the cause or nature of the state, and the other (弱) names the resulting condition, together painting a complete picture of debility, feebleness, or a profound lack of strength.