IPA: /ˈoʊvərˌnaɪtər/
KK: /ˈoʊvərˌnaɪtər/
A person who stays somewhere for one night, often while traveling.
We booked a hotel for our trip, and we had an overnighter there before continuing our journey.
Overnighter → It is formed from "over" (meaning during the whole of) and "night" (from Old English "niht", meaning the period of darkness). The word "overnighter" refers to someone who stays for the entire night.
Think of someone staying 'during the whole of' ('over') the 'night' — that's what an overnighter does.