We can invent one: kn-h. It’s knot-hours, which is technically correct but horrific to look at. It’s like the time I came across hp-h (horsepower-hour) to measure gasoline energy.

Quite standard, actually. If you buy a fridge over here it'd say something like "150 kWh/a", which is 17.12 Watts, which is how much the fridge uses on average. People don't pay for Watts, though, but for kWh, that's what's on the bill so kWh/a is way more practical if you want to convert to €/a. Also if you put more than one number in Watts in the docs civilians might get confused, ideally the only one you put there is connection power.

What’s a hectare?

I actually have no idea. I know that it's what farmers pick up women with but I have no real mental image of how much it is. 100m, sure, make that a square but it's still somehow without meaning.

but I went into a cold sweat thinking about all the awful things that would happen with a 25 mm inch,

Blame the Swedes, or more precisely Carl Edvard Johansson, inventor and manufacturer of gauge blocks. Before that the US and Brits had slightly incompatible definitions of inches and he split the difference pretty much in the middle and rounded a bit and ended up producing 25.4mm gauge blocks, and only after that industry even started to be precise and actually adhere to proper measures -- without wide availability of reference gauge blocks that was impossible. He should've rounded just a bit further.