Just recently I was in a conversation with a number of UK mainlanders and we had a debate over what "tories" meant, apparently disproportionately ordinarily it refers to a political party and it's not usual to use it as short for "territories" as I've used it (according to how the debate ended, it was half and half between them). And once again I'm reminded of how people feel to look back at their usage of a word/phrase over the years and cringe.
More tragically, me and a friend were embarrassed once upon realizing everyone was confusing "encephalitis" with "hydrocephalus" when talking to someone about their kid with hydrocephalus. Awkward because encephalitis is caused by HIV.
It took me until graduate school to learn that "mortified" is not another word for "scared"/"fearful"
It still looks that way to me what with mort in there!
It also took me a long time to realize that the word "awry", which I read often in books and inferred its meaning, and "ah-rai" were the same thing. I thought awry was pronounced "aw-ree" and it was just a synonym for "ah-rai".