clack (v.) Look up clack at Dictionary.com
mid-13c., not in Old English, from Old Norse klaka "to chatter," of echoic origin; compare Dutch klakken "to clack, crack," Old High German kleken, French claquer "to clap, crack (see claque). Related: Clacked; clacking.
clack (n.) Look up clack at Dictionary.com
mid-15c., from clack (v.).