plain; informal; suitable; convenient; opportune; to urinate or defeca
Phonosemantic compound. 亻 represents the meaning and 𠓥 represents the sound. Originally written as 𠓥, which depicted a hand holding a whip with the 丙 component. Based on the original meaning "whip a person", now written as 鞭. The current meaning is a phonetic loan.
《說文》：“便，安也。人有不便，更之。从人、更。”
whip a person