a way of buying a new car, television etc in which you give the seller your old car etc as part of the payment, or a car etc given as part of the payment for something new; = trade-in AmE:
• He sold the car in part-exchange for another vehicle.
— part-exchange verb [transitive] :
• We have fully warranted used sports cars for sale that have been part-exchanged for other vehicles in our stock range.
Financial and business terms. 2012.