Exonuclease

Exonucleases are enzymes (found as individual enzymes, or as parts of larger enzyme complexes) that cleave nucleotides one at a time from an end of a polynucleotide chain. These enzymes hydrolyse phosphodiester bonds from either the 3' or 5' terminus of a polynucleotide molecule.
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Exonuclease /exo·nu·cle·ase/ any nuclease specifically catalyzing the hydrolysis of terminal bonds of deoxyribonucleotide or ribonucleotide chains, [more]Exonuclease - Community and Resources

Noun
1. a nuclease that releases one nucleotide at a time (serially) beginning at one of a nucleic acid
(hypernym) nuclease

An enzyme that cleaves nucleotide bases sequentially from the free ends of a nucleic acid (DNA or RNA).

A nuclease which degrades a double-stranded DNA molecule by removing nucleotides from its two ends.