From Longman Dictionary of Contemporary Englishknock something ↔ together phrasal verb informalMAKEto make something quickly, using whatever you have available We should be able to knock something together with what’s in the fridge (=make a meal from items of food in the fridge). → knock→ See Verb table
Examples from the Corpus
knock together• The only other ingredient needed was some one to knock it together.• He caught hold of the two nearest him and knocked their heads together, kicked two more and grabbed the ringleaders.• She'd just box a few ears, knock a few heads together like she did with the Rattries, and chase them off. 