surname Cao; Zhou Dynasty vassal state
Phonosemantic compound. 㯥 represents the sound and 曰 represents the meaning. Depicts a pair (㯥) of people speaking (曰) against each other, i.e. a plaintiff and a defendant. The meaning later expanded to "of the same generation".
《說文》：，獄之兩曹也。在廷東，从，治事者，从曰。”