be moist, be wet
隰 centers on being moist or wet, describing a state of dampness or saturation.
隰 combines the mound radical ⻖ with 㬎, which likely contributes the sound and relates to dampness or low-lying wet ground. The exact historical development is uncertain.
The left side ⻖ suggests a mound or hill, and the right side 㬎 looks like threads (幺) under the sun (日) with fire (灬) below, as if moisture is being drawn out. Picture a damp hillside where the ground stays moist.
For シツ, imagine a wet sheet (シーツ, shiitsu) draped over the mound: sheet -> シツ, and the dampness soaks through.