swing·er 
(swĭngər)
(swĭngər)n.
1. One that swings: a good swinger of baseball bats.
2. Slang
a. A person who actively seeks excitement and moves with the latest trends.
b. A person who engages freely in promiscuous sex.
c. A member of a couple, especially a married couple, who exchanges sexual partners.
- postmenopausal
- postmenstrual
- postmeridian
- post meridiem
- postmillenarian
- postmillenarianism
- postmillennial
- postmillennialism
- postmillennialist
- postmillennian
- postmistress
- postmodern
- postmodernism
- postmodernist
- postmortem
- post mortem
- postmortem examination
- postnasal
- postnasal drip
- postnatal
- postnatally
- postnuptial
- postnuptially
- post office
- post office box