This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 濅 is uncertain. It visually contains 氵 (water) and a complex right side with 宀, 巾, and 又, but the original component relationships are unclear.
The left side is water 氵. The right side looks like a roof 宀 over a cloth 巾 and a hand 又. Imagine water seeping under a roof, soaking a cloth held by a hand—this suggests the idea of moistening or soaking, which fits the given readings.
For シン, picture the water 氵 seeping into a thin シン (thin) cloth under the roof: thin -> シン, and the cloth gets soaked.