enzymes that cut internal bonds of a polymer. Endonucleases are able to cleave phosphodiester bonds within a nucleic acid chain by hydrolysis either randomly or at specific base sequences (cf. restriction enzymes).
PAC, 1992, 64, 143. 'Glossary for chemists of terms used in biotechnology (IUPAC Recommendations 1992)' on page 152 (https://doi.org/10.1351/pac199264010143)