chat [ME] In medieval times chat was formed as a shorter version of chatter, which itself started life as an imitation of the sound made by people chatting away, rather as jabber [LME] and twitter [LME] imitated the sound they described. The chattering classes [L19th] are liberal, well-educated people, often working in the media, who are fond of expressing their views on any and every subject. See also jargon.