An Etymological Dictionary of the German Language/Annotated/Klaff
Klaff, masculine, ‘crash, yelp, bark,’ from Middle High German klaf (genitive klaffes) and klapf, masculine, ‘report, crack,’ Old High German klaph, masculine, anaklaph, ‘shock’; Middle High German klaffen, klapfen, ‘to ring, resound,’ ûf klaffen, ‘to break asunder, open, gape,’ Old High German chlaphôn; Gothic *klappôn is wanting; Anglo-Saxon clappian, English to clap. ‘Resounding’ is the primary meaning of the stem klapp, while ‘cracking, bursting, gaping’ is the derivative sense; compare Klapp and klopfen.