Obviously could mean something else if you're talking to someone whose system of notation swaps the glyphs for 3 and 4, or who uses "times" to mean what we mean by "plus"; but beyond that?

The fact that you claim to get 7 digits of accuracy by multiplying two 4 digit numbers is very questionable. If I would go after my physics textbook 1234 times 4321 = 5332000 would be the prefered answer and 1234 times 4321 = 5332114 would be wrong as the number falsely got 3 additional digits of accuracy.

A more exotic issue is whether times is left or right associative. The python pep on matrix multiplication is quite interesting. It goes through edge cases such as whether matrix multiplication is right or left associative.

Obviously could mean something different in an alternate world where "human" denotes some other species or in a community where "red" is used to denote short-wavelength rather than long-wavelength visible light; but beyond that?

Red is actually a quite nice example. Does it mean #FF0000? If so, the one that my monitor displays? The one that my printer prints? On is red not a property of an object but a property of the light and it means light with a certain wavelength? That means that if I light the room a certain way the colors of objects change. If it's a property of the object, what's when the object emits red light but doesn't reflect it? Alternatively red could also be something that triggers the color receptors of humans in a specific way. In that case small DNA changes in the person who perceives red alter slightly what red means. But "human red" is even more complex because the brain does comlex postprocessing after the color receptors have given a certain output.

If red means #FF0000 then is #EE0000 also red or is it obviously not red because it's not #FF0000? What do you do when someone with design experience and who therefore has many names for colors comes along and says that freshly spilled human blood is crimson rather than red? If we look up the color crimson you will find that Indiana University has IU crimson and the University of Kansas has KU crimson. Different values for crimson make it hard to decide whether or not the blood is actually colored crimson.

Depending on how you define red mixing it with green and blue might give you white or it might give you black.

I used to naively think that I can calculate the difference between two colors by calculating the Hamilton distance of the hex values. There even a W3C recommendation of defining the distance of colors for website design that way. It turns out it you actually need a formula that's more complex and I'm still not sure whether the one the folks gave me on ux.stackexchange is correct for human color perception. Of course you need to have a concept of distance if you want to say that red is #FF0000 +- X.

I also had lately on LW a disagreement about what colors mean when I use red to mean whatever my monitor shows me for red/#FF0000 because my monitor might not be rightly calibrated.

You might naively think that the day after September 2 is always September 3. That turns out not to be true. There also a case where a September 14 follows after a September 2. Some people think that a minute always has 60 seconds but the official version is that it can also sometimes have 61. It get's worse. You don't know how many leap seconds will be introduced in the next ten years. It get's announced only 6 months in advance. That means it's practically impossible to build a clock that tells the time accurately down to a second in ten years. If you look closer at statements things usually get really messy.

The US airforce shoot down an US helicopter in Iraq partly because they don't consider helicopters to be aircraft. Most of the time you can get away with making vague statements for practical purposes but sometimes a change in context changes the truth value of a statement and then you are screwed.