gradually, step by step, little
寖 centers on gradual, incremental progress: something happening step by step, little by little, or slowly accumulating over time.
寖 combines 宀 (roof) with 浸 (soak, immerse). The roof likely suggests something happening under cover or indoors, while 浸 contributes the idea of gradual permeation, together expressing step-by-step progress.
Under a roof (宀), water (氵) slowly soaks in (浸) — imagine a leaky roof dripping water that gradually spreads across the floor, little by little.
For シン, picture a thin (シン) stream of water slowly soaking through the roof: thin -> シン, and the water gradually spreads.