'1920s-era' originates from Modern English, specifically the combination of the numeral '1920s' (indicating the decade) and the noun 'era', where 'era' meant 'a fixed point in time' or 'period'.

'Era' entered English from Medieval/Old Italian or Old Provençal (Italian 'era'), ultimately from Latin 'aera'; numeric-decade notations such as '1920s' became common in English usage in the late 19th and early 20th centuries, and forming adjectival compounds like '1920s-era' is a 20th-century development.

Initially, 'era' meant 'a fixed date or epoch' in earlier uses, and over time it broadened to mean 'a period of time'; combining 'era' with a decade label preserved and focused that time-period meaning to indicate relation to the 1920s.