TO DISAPPOINT - [verb] to make somebody feel unhappy, because things are not as good as they hoped them to be
Examples of use
The king was disappointed at losing the battle.
I was disappointed to hear that she had failed her driving test again.
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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