Collocations used in idiomatic ways Collocation is the way in which particular words tend to occur or belong together. Collocation can also mean two or more words that go together.It sounds right to native speakers who use them all the time. Other combinations may be unnatural and just sound 'wrong'. For example, you can say: Meals will be served outside on the terrace, weather permitting. But not: Meals will be served outside on the terrace, weather allowing. "Allow and permit have very similar meanings but in this combination, only permitting is correct. It collocates with weather. We say, the fast train not quick train. Fast food not quick food. A quick shower not a fast shower. A quick meal not a fast meal. Some collocations that fall under idiomatic expressions: Achille's hill meaning: A small but important weakness in a person. E.g Favour's achille's hill is her spellings. To rack one's brain: (rack and brain collocates) meaning: to think hard E.g Y...