dimple
靨 centers on a small indentation on the face: a dimple, especially one that appears when smiling.
靨 combines 厭 (which can suggest pressing or suppressing) with 面 (face), likely indicating a pressed or indented spot on the face. The exact historical development is uncertain.
The outside 厭 looks like a pressing force, and inside is 面 (face). Imagine pressing a finger gently into a cheek to create a dimple.
For ヨウ, picture a dimple appearing when you say 'yo!' with a big smile: yo -> ヨウ, and the dimple shows on your face.