1. complex natural compound: a complex natural substance that has a globular or fibrous structure composed of linked amino acids. Proteins are essential to the structure and function of all living cells and viruses.
2. food rich in protein: a food source that is rich in protein molecules a balanced diet of fresh vegetables, fruit, and protein
[Mid-19th century. < French< Greek prōteios "primary" < prōtos "first"; from its importance to the proper functioning of the body]
