FORMIDABLE - [adjective] great and powerful, so that you feel respect or fear
Examples of use
I couldn't move anymore, when I heard his formidable voice behind me.
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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