Nikhil is a Sanskrit word. It is frequently used in Hindi, Marathi, Bengali, and other Sanskrit-derived languages. It is a very common name in India.
Sanskrit fragmentation of the word yields: Ni (without) + Kh (sky or boundary) + L (agreed or liked). It can sometimes refer to "perfection" or "perfectionism". It also means "complete" or "whole". Also the word "nikhil" came in old ayurved samhitas like Sushruta Samhita, where it denotes the meaning "entire".