Noun

1. An essentially equal exchange of two comparable things.
2. A financial derivative in which two parties agree to exchange one stream of cashflow against another stream.

Verb

1. To strike, hit.
   • 1485, Sir Thomas Malory, Le Morte Darthur, Book VI:

     and therewith was the knyght and the lady on one side – and suddeynly he swapped of the ladyes hede.

2. To exchange or give something in exchange for something else.