One who stands as an example to the rest of the world in human life is referred to as peruma:l and is worshipped as well. The illustrious and righteous Rama was given the title of peruma:l as He showed that a man can exist with all virtuous qualities.  ‘perum’ means big and ‘a:l’ means person.

Detailed Explanation: ‘perum’ means big and ‘a:l’ means person. It’s a title given to Lord Rama who being a man existed with all virtuous qualities. The illustrious and righteous Rama, followed the code of conduct to the tee and was a model for everyone in the society. Even the devatas adored him and continued worshipping him  after he slayed Ravana. One who lives a human life and makes himself a model for the society is referred to as peruma:l and will be worshipped by everybody including the de:vata:s. One who exemplifies himself to the rest of the world is called peruma:l and is worshipped as well.. 

Ko: is the supreme boss and ‘il’ is his place. God is our path finder and is our boss. So the place where God stays is ko:yil. 

Detailed Explanation:  Ko: is the supreme boss and ‘il’ is his place. God is our path finder and is our boss. So the place where God stays is koyil. Ko: also means Garuda. So ko:yil also means Garuda’s place. Garuda is the representative of Ve:das. So wherever vedas stay, is also where the ve:da ve:dya (God) stays. So that place is where God stays and is ko:yil

But now it refers to all temples. Some people worship Vishnu, some Lord Shiva, Shakti, Ambal  and some other forms for other people . But whatever form is worshipped, that is the one that leads the life of those people and becomes their boss. The place where their boss stays becomes their ko:yil. The word was fundamentally only used for Vishnu temples but now it is also used for temples for other forms such as sivan koyil. Amman koyil etc.