peaceful
靖 centers on a state of calm stability: peaceful, tranquil, and settled. It describes a condition where things are quiet and undisturbed.
靖 combines 立 (stand) and 青 (blue/green, also associated with clarity and purity). The character likely expresses the idea of standing in a clear, settled state, hence peace and tranquility. The exact historical development is uncertain, but the component combination suggests a settled, upright calm.
Imagine standing (立) under a clear blue (青) sky, feeling completely peaceful and still. The scene is calm and undisturbed.
For セイ, picture a peaceful scene where you say 'say' (セイ) nothing—just enjoy the quiet. 'Say' cues セイ, and the silence matches the peaceful meaning.