Merriam-Webster Collegiate Dictionary - clack

 I. verb  Etymology: Middle English, of imitative origin  Date: 13th century  intransitive verb  1. chatter, prattle  2. to make an abrupt striking sound or series of sounds  3. of fowl cackle, cluck  transitive verb  1. to cause to make a clatter  2. to produce with a chattering sound; specifically blab  • ~er noun  II. noun  Date: 15th century  1.  a. rapid continuous talk ; chatter  b. tongue  2. archaic an object (as a valve) that produces clapping or rattling noises usually in regular rapid sequence  3. a sound of ~ing the ~ of a typewriter