ヨウ, い.る, かなめ, とし
need, main point, essence, pivot, key to
JLPT3 G4 S9 F106
The relevant bronzeware inscription form is 女 woman + an element combining a pair of hands and a backbone → compress a woman's waist, creating curvaceous hips → waist; hips → *main point*; *vital* (← hips as the pivot point of the body) → *brief*; *sum up*; *in short*. Also, *demand* (← demand that which is vital to one) → *want*; *need*; *require*.
[Full Kanji Etymology List]