An Etymological Dictionary of the German Language/Klaff
Klaff, m., ‘crash, yelp, bark,’ from MidHG. klaf (gen. klaffes) and klapf, m., ‘report, crack,’ OHG. klaph, m., anaklaph, ‘shock’; MidHG. klaffen, klapfen, ‘to ring, resound,’ ûf klaffen, ‘to break asunder, open, gape,’ OHG. chlaphôn; Goth. *klappôn is wanting; AS. clappian, E. to clap. ‘Resounding’ is the prim. meaning of the stem klapp, while ‘cracking, bursting, gaping’ is the derivative sense; comp. Klapp and klopfen.