Compare French claque (“a slap or smack”).
clack (plural clacks)
- an abrupt, sharp sound, especially one made by two hard objects colliding repetitively; a clatter; in sound, midway between a click and a clunk
- Anything that causes a clacking noise, such as the clapper of a mill, or a clack valve.
- chatter; prattle
- Whose chief intent is to vaunt his spiritual clack.
Derived terms 
- (intransitive) To make a sudden, sharp noise, or succession of noises; to click.
- We heard Mr. Hodson's whip clacking on the shoulders of the poor little wretches.
- (transitive) To cause to make a sudden, sharp noise, or succession of noises; to click.
- To chatter or babble; to utter rapidly without consideration.
- (Can we find and add a quotation of Feltham to this entry?)
Part or all of this entry has been imported from the 1913 edition of Webster’s Dictionary, which is now free of copyright and hence in the public domain. The imported definitions may be significantly out of date, and any more recent senses may be completely missing.