Is there a word for a word that someone hears often but never has learned the formal definition to and can only guess the meaning of from the contexts it has been used in? I know I've been in the position in which I've heard a word used so often I haven't consulted a dictionary and so I didn't know the real definition and would struggle every time I heard it to figure out what it means really.
An offshoot of my question is: is there a word for a word that someone thinks one knows the definition to, but is actually incorrect? I've also seen this phenomenon a lot, where someone thinks he knows the definition and uses it just incorrectly enough for me to tell he doesn't really know what it means.
This is two questions, and you shouldn't post two questions under the same post, it will just cause confusion. Anyway:
Re 2., you could call it a misapprehension, which means that you think you understand something when actually you have the wrong idea.