"make a quick, sharp noise," 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.)
"a sharp, repeated, rattling sound," mid-15c., from clack (v.).
civilized
civilly
civvy
clabber
clachan
clack
clad
claddagh
clade
cladism
cladistic