When I was in elementary school, one of my classmates pronounced it "thermo meter" and I had to watch the science teacher struggle for a good 30 seconds to decide if he was going to correct him or not.
Most other languages do call it a thermo meter or similar. People who are not native English speakers will pronounce it wrongly when speaking English, because the word is the same - it's just pronounced weirdly in both British and American English. The British and American pronunciations are not exactly the same on this, but they're both wrongdifferent from any other languages, except Greek.
The English pronunciation is caused by English inheriting the Greek way of stressing the third last syllable on words of Greek origin. It makes no sense in my mind why they do it on compound words though. Meter is not Greek. It's English, so they could've chosen differently, but they obviously chose the most annoying way to pronounce it.
There's a few other words like that, but I don't remember which..
Hah. That reminds me of a joke I used to play on my wife back when cars had cd players. After we got in the car, about once a month I would come up with
Seriously though i did not understand which one I am pronouncing. I would usually read thermo meter and thermometer the same. When I try to differentiate by trying to make it sound together, or by trying to make more detatched, i just can't and end up pronouncing the same