1. The change of the use of something to another use; or the change in religious beliefs from one religion to another. English = conversion.
2. [With stress] A complete change in something. English = transformation.
3. Something which is given to someone at the same time they give you something. English = exchange.
4. A business deal in which someone buys a new car, washing machine, etc. at a reduced price by giving an old car, washing machine, etc. as well as money in payment. English = trade in.