Why is it called a manhole in the first place and not a sewer hole or just a hole? I always just called it "the sewer" growing up. Had to fish some keys out of it once. That was hard.
Yeah, and why's this called a porthole? https://en.wikipedia.org/wiki/Porthole
If there are some of these on both sides of a ship, shouldn't half of them be called starboardholes?
I think it comes from very ancient times when you only docked your boat while in "port" on the "port" side because the rudder was on the starboard side of the vessel instead of the middle as in modern ships. Originally, "port" was called larboard but this was too easily confused with starboard when shouted into a gale force wind. A port hole was probably only opened while in "port" to avoid sinking in heavy seas.
I think that's it. If you look up the etymology of "port", you get;
1. The Latin "portus", which means harbor.
2. The Latin "porta", which means gate or door.
This site seems to say that "porthole" was derived from "porta", which makes sense to me.