I have checked in google keywords Tool there were 1120000 results for the word 'free movie' and 1100000 results for the word 'free movies'. So, should I use both the keywords in my meta keywords tag or one of them. If one them which one?
I wouldn't worry too much about meta keywords. Focus on more important factors like website structure, internal/external linking. You probably checked the keyword volume on broad match. On the left, select exact match and I bet you the plural version comes first. I would go with that if you really want to.