Princeton's WordNet

1. knockdown(adj)

   a blow that knocks the opponent off his feet

2. knock-down(a), powerful(adj)

   strong enough to knock down or overwhelm

   "a knock-down blow"

3. knockdown(verb)

   (furniture) easily assembled and dismantled

   "I bought a knockdown chest at the do-it-yourself store"

4. down, knock down, cut down, push down, pull down(verb)

   cause to come or go down

   "The policeman downed the heavily armed suspect"; "The mugger knocked down the old lady after she refused to hand over her wallet"

5. deck, coldcock, dump, knock down, floor(verb)

   knock down with force

   "He decked his opponent"

6. blast, knock down(verb)

   shatter as if by explosion