'peptidic' originates from the noun 'peptide' combined with the adjectival suffix '-ic'. 'Peptide' itself comes from modern scientific coinage based on Greek roots 'pept-' from Ancient Greek 'pēptein' meaning 'to digest'. The suffix '-ic' comes from Greek '-ikos' via Latin/Old French meaning 'pertaining to'.

'Peptide' was formed in modern scientific nomenclature (late 19th–early 20th century) from Greek roots related to digestion; English then formed the adjective 'peptidic' by adding the productive suffix '-ic' to mean 'pertaining to peptides'.

Initially the Greek root related to digestion ('to digest'), and when adopted into modern chemistry/biochemistry it came to denote short chains of amino acids; 'peptidic' now specifically means 'relating to peptides' rather than general digestion.