シツ, シュウ, しめ.る, しめ.す, うるお.う, うるお.す
damp, wet, moist
JLPT2 G7 S12 F1517
The relevant oracle bone form of this character is 水 water + an element# representing bundles of thread pressed together → soften bundles of thread by submerging them in water → *wet*; *moisten*; *damp* → *rain*. There is no etymological connection with the 㬎 element described in 顯.
[Full Kanji Etymology List]