'nonreptilian' originates from the English negative prefix 'non-' (from Latin 'non', meaning 'not') combined with 'reptilian', which ultimately comes from Latin 'reptilis' (from 'repere' meaning 'to creep').

'reptilis' in Latin (meaning 'creeping') passed into Medieval/Modern Latin and Old French forms and gave rise to English 'reptile' and the adjective 'reptilian'; the English prefix 'non-' has long been used to form negations, and the compound 'nonreptilian' is a modern English formation combining these elements.

Initially, Latin 'reptilis' meant 'creeping'; over time it developed into the noun 'reptile' and the adjective 'reptilian' describing animals of that group. 'Nonreptilian' later emerged to denote 'not reptilian' in literal and extended senses.