On Feb 5, 2013 the question "Can anyone provide a comprehensive but structural and functional reality based definition of protein?" was put by me as it was felt that there are plenty of sources defining protein, but something is missing somewhere. There are only two responses till date, one of which is from one of my coworker. Finally I decided to provide an answer myself and worked on it. But I want to present the answer with a prelude to describe how the question arose and what is the expected utility of the answer. As it is a bit lengthy, it is presented as an attached word file. Interested friends may go through and interact with opinion, comment, criticism and suggestions for modification.