quiet
靜 centers on stillness and absence of noise: a state of quiet calm. The meaning is straightforward and does not branch into unrelated senses.
靜 is the traditional form of 静. It combines 青 (blue/green, here likely contributing the sound) with 爭 (to contend), but the exact semantic role of 爭 in expressing 'quiet' is uncertain. The modern Japanese simplified form 静 replaces 爭 with 争.
The left side 青 suggests a calm, clear blue sky, while the right side 爭 looks like a hand reaching for something. Imagine a hand raised to hush a crowd under a blue sky, bringing quiet.
For セイ, picture a serene blue lake (青) where you say 'say' very softly: say -> セイ, and the quiet scene stays still.