On point number 3, I once got dunked on for saying that I didn't know anything about the subject at hand when asked. The other person told me "Well, that's just a cop out. Just make something up!"
The general meaning is the appearance of truth or validity.
But I usually use it to describe something that is "believable" even if the underlying premise is not. So a fantasy story that pays close attention to detail and is highly consistent might be described as having versimilitude. On the other hand, a story where the characters make out-of-character choices might be lacking versimilitude, even if there are no overtly "fictional" elements to the story.
That's usually how I've heard it used, not sure if it's the "main" usage though.
If we were honest, it's the thing we should all be saying and hearing all day long. But it's not. Quite the opposite, it's among the rarest. Instead, people are shooting their certainties at one another, relentlessly.
Not knowing something or not having an opinion on a question is not an issue. It's to be expected, even if we were all geniuses (I'm certainly not one). Not doing the work to inform oneself could potentially be an issue but should not be as long we don't pretend otherwise. It's when one pretends to know, based on what one has heard someone else say, or because one wants to push a specific narrative that suits them, that shit starts hitting the fan. That's when living together turn into the stinking shit hole it has turned into in which lies are fine (when they're not adored) and facts have become suspicious if not dangerous.
For me, the small politeness words are not "thank you", "sorry", or "good morning". They're "maybe", "I think", "perhaps", "I don't know". I respect honest doubt way, way more than I respect dishonest = rushed certainty, and I wish I saw more of that.
Does just broader vocabulary count? Maybe it's just a rule that everyone sits down with a dictionary every couple of weeks for 30 minutes just opening it to a random page.
Knowing the word would ideally be due to people knowing the meaning of it, which most people can't grasp. Especially important for most political actions, such as tariffs and climate change.
not hear, but read…see?: aluminium, your is possessive and you’re is you are (IT’S NOT THAT HARD IF YOU ARE FLUENT IN ENGLISH), it’s vs its (NOT THAT HARD EITHER FOR NATIVE SPEAKERS)