Asklemmy

Since OP is in the UK, I can pull out “nonplussed.” Current American usage of the word is a lack of surprise or general acceptance. I am nonplussed when news arrives that another politician was caught in a sex scandal. Non-American usage is complete surprise and an inability to act. The Scot was nonplussed when the drunk American vomited noisily on his shoes.

Edit: I am firmly in the “general acceptance” camp and usually have to process for a second or two when someone uses it in its traditional sense.

When I was younger I thought concur meant disagree.

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".

Terrence Thatcher, T. May, Terroris, Ttruss;
Terry-Tories, Terry-Tories, make a fuss!

It also gives a different meaning to the citizens of British Overseas Tories!

ages ago, i spent something like half a year thinking there was a word "appericate". it was an odd one, since i only ever saw it in print, and from context it was clear that it meant the same thing as "appreciate", which, oddly enough, i only ever heard in speech.

and then one day i stopped at an "appericate" in a book and re-read it 9 times, very slowly.

Man, I'm learning some weird stuff about British people. I've never heard of encephalitis being associated with HIV or a nonce being any kind of person.

"Sorry."

I don't use it very often but I misuse the word "Gattaca" on purpose sometimes. In reality it's the title of the 1997 film that's named from the letters G,A,T, and C, referring to guanine, adenin, thymine and cytosine, the four nucleobases of DNA.

But on the TV show The League, the character Rafi (Jason Mantzoukas) screams it as his battle cry during paintball, completely oblivious to what it actually means or that it's the title of a movie. I urge you all to misuse this word at some point as well -- if you ever need to hype yourself up, try screaming "GATTACA!" as your battle cry!

Inconceivable!

With English as my second language, the difference between terrible and terrific has always confused me.

Callow. It just means immature but I somehow got it in my head that it meant cowardly.

The word "nauseous" is parallel to "noxious" and means "causing nausea". If you're experiencing nausea, you're nauseated -- the thing that made you nauseated is nauseous.

Not a word but I thought the idiom toe the line meant basically the same as push the envelope. As in you're testing the boundaries of something by walking right up to the line and nudging it with your toe to move it further.

Turns out it means pretty much the opposite, essentially the same as fall in line.

Portuguese ⟨bisonho⟩. I always used it as "needy", "demanding excessive attention" (like a child). Until someone informed me that it was supposed to be "weird".

Depreciate.

I'm going to Depreciate this computer. That means to get its loss of value on taxes....not to shut it down. The word I meant was Deprecate

I mean, homonyms exist, confusing them/not knowing a word has one doesn't make it "wrong". Surely you (e: plural, not having a go at you op lol) could tell tories and Tories apart by context (if not capitalisation)?

Redux. I've always just used it as a fancier 're-do'. Still going to keep using it as such. I like the word too much.