萎 can be used literally (plants withering) or figuratively (a person becoming dispirited or listless). In compounds: 萎缩 (to shrink/wither), 萎靡 (dispirited / sluggish).
Three-stroke grass radical on top, the indexing radical. 萎 means to wither or wilt - what a plant does when starved of water. Groups with 枯 dried up, 凋 to wither, 谢 to drop, 荒 desolate. The char also extends to dispirited people.
Bottom 委 supplies the sound - wěi read straight across with no shift. 委 also pulls a semantic thread: it pictures grain bending under its own ripe weight, and from there means to droop. So grass on top of a drooping plant gives the wilting image directly.
