Add the word Xerus

[vaibhavijha]

Add all the definitions of [Word] in a file named [Word].json in folder [First-Letter]

Refer CONTRIBUTING.md for more details on how to contribute.

Comment the words you'll be adding if you're are working on this issue to avoid conflicts.
Add reference to this issue i.e Issue # in your pull request description.

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[Rishabrp99]

hey @vaibhavijha , i would like to add the word Xerus in isssue #3391.Can you please assign it to me???