Hello Sujal,

You can checkout ssbcrack's website for the antonyms and synonyms for NDA exams, they have previous year questions and also possible questions.you can prepare from there, or you can buy study materials from different coaching platforms specific to English, they will cost you less and help you alot in your preparation.

Also you can give mock tests to test your knowledge so that you can prepare well.

I hope it helps,

Best of luck