'30s' originates from Modern English, formed by the numeral '30' (thirty) plus the plural/decade-marking suffix '-s'; 'thirty' itself comes from Old English 'þrītig', where 'þrī(e)' meant 'three' and '-tig' meant 'ten'.

'30s' developed as a written abbreviation in modern usage to refer to decades or plural ages (for example, 'the 1930s' or 'people in their 30s'). The underlying word 'thirty' evolved from Middle English 'thirty', which in turn came from Old English 'þrītig'.

Initially 'thirty' meant literally 'three tens' (the number 30). Over time the form '30s' emerged as a shorthand notation to denote the decade of years ending in the 30s or the age range 30–39; this orthographic convention is a modern usage.