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early 13c., chateren "to twitter, gossip," earlier cheateren, chiteren, of echoic origin. Cf. Dutch koeteren "jabber," Danish kvidre "twitter, chirp." Related: Chattered; chattering. Phrase chattering class in use by 1893, with a reference perhaps from 1843:
Such was the most interesting side of the fatal event to that idle chattering class of London life to whom the collision of heaven and earth were important only as affording matter for "news!" [Catherine Grace F. Gore ("Mrs. Gore"), "The Banker's Wife," 1843]
mid-13c., originally of birds, from chatter (v.).