Merriam-Webster Collegiate Dictionary - knockdown

 I. adjective  Date: 1690  1. having such force as to strike down or overwhelm a bewildering assortment of ~ arguments — J. W. Krutch  2. that can easily be assembled or disassembled a ~ table  3. chiefly British extremely low ; reduced ~ prices  II. noun  Date: 1809  1. the action of knocking down  2. something (as a blow) that strikes down or overwhelms  3. something (as a piece of furniture) that can be easily assembled or disassembled