ONE WORD SUBSTITUTION

1. A person who represents a state in a foreign country = ambassador राजदूत
2. A person who does not believe in the existence of God = atheist नास्तिक
3. The yearly return of an event = anniversary सालगिरह
4. An assembly of listeners = audience श्रोतागण 
5. The life history of a person written by himself = autobiography आत्मकथा
6. The most powerful power = almighty सर्वशक्तिमान
7. A person who does something for his pleasure not for the sake of money = amateur शौकिया
8. A piece of writing whose writer in not known = anonymous गुमनाम
9. A person who cannot pay off debts = bankrupt / insolvent दिवालिया
10. Study of plants = botany वनस्पति विज्ञान
11. The life history of a person written by another = biography जीवनी
12. One who breaks out in a house = burglar सेंधमार
13. A plot of land that does not grow anything = barren बंजर
14. One who exists at the same time as another = contemporary समकालीन
15. Having constituent elements from all over the world = cosmopolitan सर्वदेशीय