Wiktionary
vb. 1 (context transitive English) To stun; to surprise. 2 (context transitive English) To drink an alcoholic beverage swiftly or often. 3 (context transitive UK Australian English) To reject; to refuse.
WordNet
Usage examples of "knock back".
How could they do anything else if they wanted to go home afterwards and kiss their wives and eat pig's knuckles and knock back a seidel or two of beer?
I've never seen you knock back a drink so fast, and I've never heard you so quiet.
There wouldn't be more than a dozen or so scattered foemen he'd have lo knock back on their heels—.
I'm not saying no one will ever come up with a doctrine which won't at least knock back Apollo's effectiveness.
My few more direct enquiries about those times, even when I forced myself to stay late in the Bacton Arms and knock back slippery pints of Coxly's, were met with blank stares or dark hostility.
There was only one ship in the galaxy that could knock back a blip that big at such a distance.