'archaising' originates from Greek, specifically the word 'arkhaios', where 'arkhaios' meant 'ancient'. The modern English verb 'archaize/archaise' (and its participle 'archaising') is formed with the English verbal suffix '-ize/-ise' attached to the adjective 'archaic'.

'arkhaios' (Greek) passed into Late Latin as 'archaicus' and through Old French/Middle English as 'archaic'. From the adjective 'archaic' the verb 'archaize' (also spelled 'archaise') was formed in English by adding '-ize/-ise', and the contemporary participle form became 'archaising' (UK) / 'archaizing' (US).

Initially, the root meant 'ancient' or 'from the beginning'; over time, it evolved into an adjective meaning 'old-fashioned' or 'pertaining to an earlier period', and then into a verb meaning 'to make or render something archaic'—the participle 'archaising' expresses that action or quality.