SUPPLEMENT - [noun] something additional, something extra
Examples of use
The money she earns translating documents is just a supplement to her main income.
If you want to use the hotel swimming pool and sauna, you will have to pay a supplement to your accommodation.
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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