核心畫面
Think of something hanging loose and moving from side to side, never settling on one spot. Both meanings of swinger can be read as a person seen that way: not fixed in one place, moving with whatever is happening. One sense puts that movement into a social life, the other into relationships.
可以想成一樣東西鬆鬆地掛著，左右來回擺，從不停在同一點上。swinger 的兩個意思，都可以當成「被這樣看待的人」：…更多收起
可以想成一樣東西鬆鬆地掛著，左右來回擺，從不停在同一點上。swinger 的兩個意思，都可以當成「被這樣看待的人」：不固定在一個地方，跟著當下的熱鬧走。一個意思把這種擺動放在生活方式上，另一個放在伴侶關係上。From the word’s history
Recorded as swing + -er: the one who swings, with -er marking the person who does it.
來源記為 swing（擺動）加上 -er，也就是「做這件事的人」。這只是一條字面上的線索，怎麼從擺動走到今天的用法，這裡不做歷史上的斷定。
Wiktionary/kaikki extract for swinger (etymology 1): From swing + -er (source_ref kaikki:3f6f69a190036ae4:1187470841:15695)