The word Nanak has been taken from Sikhism and it conveys the idea of the most revered guru of the Sikhs. How he was named as such is very difficult to determine but now even the mention of the name considered as something to do with holiness.
Guru Nanak Dev was the founder of Sikhism and the mission behind founding this sect was to wipe out the caste system that was prevailed in Hindu society during those days. Now he is not only revered by the Sikhs but Hindus and Muslims of Indian subcontinent equally respect him.
He was the first of the ten gurus that are considered as the pillars of Sikhism and it is his teachings that every Sikh follows in his life.
Right now I am listening to a sakhi (teaching) explaining how Guru Nanak Dev ji was named. So when he was born, his father (Mehta Kalu, from a Khatri family) went to the priest and asked him to name his son. When the priest saw his son, he was in deep thought starting to wonder what to name him. He said that this boy here will guide the world in the right direction. Mehta Kalu was amazed. Mehta Kalu said why don't you name him according to his birth chart and according to the first sound he made when he stepped into the world. The priest said that he would make the birth chart but he asked what was the first sound he made. Mehta Kalu said that he didn't pay attention to that. So, they decided to ask the midwife. The midwife said that he amazed me, it was the most different sound I'd have ever heard. She said, that he laughed when he stepped into the world. Out of all the babies I've helped with, he had the most different sound. And, the laugh wasn't even child-like, it wasnt a laugh of a child, it was a laugh of an adult. The priest and the father thought that he probably laughed because he wanted to tell everyone that he's here with a message from god. The message was "Ek onkaar Satnam.....", it is the answer to all problems. When he saw the son, he said to Mehta Kalu that he is a lucky man to have had such a lucky boy. Mehta Kalu asked the priest to name him. The priest said that he will need to think about his name very deeply. He replied to the father and said that he will tell him in 13 days. On the 13th day, the priest went to their house and said that he should be named Nanak. Mehta Kalu said that we can't name him that because "we are khatris and we havent heard of a name like this before, name him something that is appropriate according to our religion". The priest replied that the boy is not a normal person, his name will be on everyone's lips, clouds, land, water will all pay his heed,everyone will listen to him. Mehta Kalu is very amazed and didnt argue any further and said that alright he will be named Nanak. The priest said that there are 2 reasons for this name. First of all, in Sanskrit if you break down the name,it is na-an-akhe. Na means human, an means without and ake means pain. One who doesn't have any pain. In Gurmukhi it is na-anake, na means not and anake means different, so he's not different, basically us humans have different ways we address God like Allah but he's still GOD. We all still call him GOD. Everyone was amazed and really happy. After this comes the sakhi about Guru Nanak Dev Ji's childhood which is also very interesting.
