ADVERSARY - [noun] an enemy
Examples of use
She was perceived as an adversary in this company from the beginning, but it took nearly 6 months for the boss to dismiss her.
Our main adversary in the market tries hard to win our clients.
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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