Knowing one's own language

For the first week of my French class the teacher gave us a number of sentences to translate from English into French. One of them struck us all as a little strange and poetic: "The house smelt of size and new paint." When we were all suggesting French words like grandeur for "size", she asked us, 'Who looked up "size" in an English dictionary?' Of course none of us had, but apparently we should have because here it referred to sizing glue.

Despite having learnt my lesson, I still felt a bit sorry for the two American girls presenting their translations in French class this week. They made a big dialectical mistake with the word "semi".

The phrase was, "The houses were much larger than Wilt's semi." The first thing that came to their American minds was a semi-trailer. I must admit, that thought occurred to me too, but I dismissed it when I realised that it had to be a type of house and inferred that "semi" must be slang for semi-detached. (Thanks, Richard Thompson!) Not these two. They had the word "trailer" stuck in their heads and - because Americans call caravans "trailers" - they inferred that the character in question lived in a caravan park.

I must admit, "semi-detached" is not a term I would use, I'd probably use "duplex" in the broader (apparently American) sense. But seeing their embarrassing mistake has reminded me to keep looking beyond my own natural vocabulary.