1.
If you knock back a drink, especially an alcoholic one, you drink it quickly, and often in large amounts. ( INFORMAL )
He was knocking back his 10th gin and tonic of the day...
She poured some vodka into a glass and knocked it back in two swallows.
PHRASAL VERB : V P n (not pron) , V n P
2.
If an event, situation, or person knocks you back , they prevent you from progressing or achieving something. ( mainly BRIT )
It seemed as though every time we got rolling something came along to knock us back...
That really knocked back any hope for further peace negotiations.
= set back
PHRASAL VERB : V n P , V P n (not pron)