The word protein was first proposed in 1844 by the Dutch chemist Gerhard Johan Mulder (1802-1880) from the Ancient Greek root proteios meaning the first quality.  Proteins are defined as biochemical compounds consisting of one or more polypeptides, usually folded into a more compact form.  Protein entered English in 1907. 

Image of hexokinase, a common protein, courtesy Wikipedia under Creative Commons 3.0 license.