'aplanaticity' originates from New Latin/modern English, ultimately formed from the adjective 'aplanatic' (from Greek components), where 'a-' meant 'not' and the root related to Greek 'planō'/'planos' conveyed the idea of 'wandering' or 'deviation' (hence 'without deviation' in optical use).

'aplanatic' entered scientific English via New Latin and French (e.g. French 'aplanatique') in descriptions of optical design; the abstract noun 'aplanaticity' was later formed in English to denote the quality or state, yielding the modern English 'aplanaticity'.

Initially formed from elements meaning 'not wandering/without deviation', the term's sense narrowed in technical use to mean 'free from optical (especially spherical) aberration', which is its current specialized meaning.