calm
穩 centers on a state of settled stillness and peace: being calm, tranquil, and free from disturbance.
穩 combines 禾 (grain) with 㥯, which likely contributes the sound and the idea of careful handling. The character suggests the calm stability of gathered grain.
Picture a field of grain 禾 on the left, and on the right a hand 爪 gently pressing down over a heart 心, keeping everything still and calm.
For オン, imagine the calm feeling of being 'on' a quiet, peaceful hill: on -> オン, and the grain sways gently in the breeze.