fǒu, pǐ
not
Originally the same character as 不. Distinguishing component 口 was added later to the character when it took on the meaning "not". 不 represents the sound.
Components
Evolution

Bronze script
Late Western Zhou (~800 BC)
Seal script
Shuowen (~100 AD)
Clerical script
Eastern Han dynasty (25-220 AD)Regular script
ModernComponent uses
Meaning component in 1 character (1 verified)
Sources
李学勤《字源》p.94-95