Complex sentence: Peptides (from Gr. πεπτός, "digested", derived from πέσσειν, "to digest") are biologically occurring short chains of amino acid monomers linked by peptide (amide) bonds.
Split into simpler sentences: Peptides (from Gr. πεπτός, "digested", derived from πέσσειν, "to digest") are naturally occurring biological molecules. They are short chains of amino acid monomers linked by peptide (amide) bonds.