CLACK, verb intransitive

1. To make a sudden sharp noise, as by striking or cracking; to clink; to click.

2. To utter words rapidly and continually, or with sharp, abrupt sounds; to let the tongue run.

CLACK, noun

1. A sharp, abrupt sound continually repeated, such as is made by striking an object, or by bursting or cracking; continually talk; as, we do not wish to hear his clack; a common expression. Hence the word is used for the tongue, the instrument of clacking.

2. The instrument that strikes the hopper of a grist-mill, to move or shake it, for discharging the corn. And according to Johnson, a bell that rings when more corn is required to be put in.

To clack wool, is to cut off the sheeps mark, which makes it weigh less, and yield less duty.