The one word for 'no longer used' is...........  

Give one word for the given phrase;- " A decision on which one cannot go back ".

Give one word substitute for 'things of different nature' : 

Give one word substitute:

The study about the cause and nature of diseases:

Our Chief Minister is a person of long experience in politics (Use one word for the words underlined). 

One who does not believe in  the existence of God is called an ---------