'apologia' originates from Greek, specifically the word 'apología' (ἀπολογία), where 'apo-' meant 'away/from' and 'logos' (from 'legein') meant 'speech' or 'reason'.

'apologia' passed into Late/Medieval Latin as 'apologia' and entered English (via Modern Latin/learned usage) with the sense of a formal speech or written defence, retaining the Greek root.

Initially, it meant 'a speech in one's own defence'; over time it broadened to include written defences and more general formal justifications of beliefs or actions.