to make flat.

to knock down

The boxer flattened his opponent in the second round.

to become flat. ?

flatten in, Nautical . flat 1 ( def. 61 ) .

flatten out, Aeronautics . to fly into a horizontal position, as after a dive.

verb

break , elevate , make uneven , raise , round

verb

abrade , beat down , compress , crush , debase , deflate , depress , even out , fell , floor , flush , grade , ground , iron out , knock down , lay , lay low , mow down , plane , plaster * , prostrate , raze , roll , smash , smooth , spread out , squash , straighten , subdue , trample , flat , level , bring down , cut down , down , strike down , throw , deck , defeat , deject , oblate , step on