We found 9 dictionaries that define the word knock on the head:

General (4 matching dictionaries)

1. knock (something) on the head, knock on the head: Merriam-Webster
2. knock on the head: Collins English Dictionary
3. knock on the head: Wiktionary
4. knock on the head: TheFreeDictionary.com

Business (1 matching dictionary)

5. knock on the head: Legal dictionary

Computing (1 matching dictionary)

6. knock on the head: Encyclopedia

Medicine (1 matching dictionary)

7. knock on the head: Medical dictionary

Miscellaneous (1 matching dictionary)

8. knock on the head: Idioms

Slang (1 matching dictionary)

9. knock (something) on the head (!): English slang and colloquialisms used in the United Kingdom

Definitions from Wiktionary (knock on the head) ▸ verb:  (transitive) To put an end to; to defeat or frustrate (a scheme or project). Similar: knock out, knock into a cocked hat, hand someone his head, brain, kill off, finish, put an end to, knock down, put paid to, block, more... Opposite: pat on back, praise, compliment, encouragement Phrases: knock something on the head, more... ▸ Words similar to knock on the head ▸ Usage examples for knock on the head ▸ Idioms related to knock on the head ▸ Wikipedia articles (New!) ▸ Words that often appear near knock on the head ▸ Rhymes of knock on the head ▸ Invented words related to knock on the head