TO SET OFF - [verb] to start a journey
Examples of use
We set off in 2000 with the aim of visiting every country in the world.
The ship set off in 2005 and nobody has seen it since that time.
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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