WordNet sense 1 (a lower limit):

base

WordNet sense 2 (a large room in a stock exchange where the trading is done):

trading floor

WordNet sense 3 (a structure consisting of a room or set of rooms at a single position along a vertical scale):

level, storey, story

WordNet sense 4 (the inside lower horizontal surface (as of a room or hallway)):

flooring

WordNet sense 5 (surprise greatly; knock someone's socks off):

shock, stun, ball over, blow out of the water, take aback

WordNet sense 6 (knock down with force):

deck, dump, coldcock