far, deep, sunken eyes, sad
窅 centers on a sense of deep, hollow distance: something far away, a deep recess, or eyes that appear sunken and distant. The sadness meaning follows from that same hollow, withdrawn feeling.
窅 combines 穴 (cave, hole) and 目 (eye), suggesting eyes deep-set as if in a cave, or a deep, far-off gaze. The exact historical development is uncertain, but the component combination fits the meanings.
Imagine a cave (穴) with a single eye (目) peering out from deep inside. The eye looks far away, sunken and sad, lost in the hollow darkness.
For ヨウ, picture a yawning cave so deep and far that it echoes: yawning -> ヨウ, and the sunken eye inside looks sad and distant.
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