A colloquy is a formal conversation.
If you collude with people, you work secretly with them to do something dishonest.
When you collate pieces of information, you gather them all together and arrange them in some sensible order in order to examine and compare those data efficiently.
When people collaborate, they work together, usually to solve some problem or issue.
Collateral is a security or guarantee, usually represented by personal property of equal value, that a borrower must put up when they take out a loan.
When something collapses, such as a bridge or building, it falls down suddenly.
When two things collide, such as cars or trains, they smash together or crash into each other.
A collection is a gathering or bringing together of things, such as coins or rocks.
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