knock somebody/something back phrasal verb informal ( see also ↑ knock )
1 . knock something ↔ back to quickly drink large quantities of a drink, especially an alcoholic drink:
Brenda knocked the brandy back quickly.
2 . knock somebody back something to cost you a lot of money:
His new car knocked him back several thousand dollars.
3 . knock somebody back British English to make someone feel upset, shocked, or physically weak