'justificatory' originates from Latin, specifically the verb 'justificare', where 'justus' meant 'just' and 'facere' meant 'to make'. The English adjective was formed by adding the adjectival suffix '-atory' to the verb 'justify'.

'justificare' (Latin) developed into Old French/Latin-derived forms such as 'justifier' and entered Middle English as 'justify' (via Anglo-Norman/Old French influences). From the verb 'justify' the adjective-forming suffix '-atory' produced 'justificatory' in later English.

Initially, the Latin root meant 'to make just' or 'to render righteous'; over time in English the sense narrowed to 'serving to justify' or 'providing justification' as an adjectival quality.