need not; does not have to; not necessarily
不 (bù) · 4 strokes
Pictograph of sepals of a flower. The modern meaning "no" is a phonetic loan.
必 (bì) · 5 strokes
Pictograph of a weapon handle, now written as 柲. 八 was later added as a decorative mark. Similar to 戈 but without the blade. The current meaning is a phonetic loan.