FAULT - [noun] responsibility for a bad situation; a problem which makes something work improperly
Examples of use
It's not our fault that we've been late. The bus was 30 minutes late.
There was a big electronic fault in the car. It's going to take a few days to repair it.
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English speaking practise
Remember that if you don't use that word in English conversations or writing you'll forget it in a short time. So the best thing you can do to learn this word is just trying to use it in speaking or writing. Remember also that practise is the key to fluent english speaking.
You can always find a partner, who would also like to improve his/her