xū
must
Original meaning:
beard
Pictograph of a person with a bearded face. Based on the original meaning "beard", now written as 鬚. The current meaning is a phonetic loan.
Evolution

Oracle script
(~1250-1000 BC)
Bronze script
Late Western Zhou (~800 BC)
Seal script
Shuowen (~100 AD)
Clerical script
Western Jin dynasty (266-316 AD)Regular script
ModernComponent uses
Sound component in 1 character (1 verified)
Iconic component in 1 character (1 verified)
Sources