The American Heritage® Dictionary of the English Language, 4th Edition
n. A macromolecule in a living organism that is formed by linking together several smaller molecules, as a protein from amino acids or DNA from nucleotides.
n. any macromolecule of a living organism that is formed from the polymerization of smaller entities; a polymer that occurs in a living organism or results from life.
Word Usage
"A biopolymer is a naturally-derived alternative to synthetic polymers, which are long molecules that join other molecules together."