The decade from 1970 to 1979; the numbers from 70 to 79.
From 'seventy' plus the plural suffix '-ies.' Old English 'seofontig' from 'seofon' (seven) + '-tig' (group of ten). The cultural association with the 1970s decade developed naturally as decades became recognized cultural periods.
The seventies as a cultural concept represents our human need to package time into meaningful units. What we call 'the seventies' - disco, bell-bottoms, social change - didn't neatly start on January 1, 1970, but the decade gives us a convenient way to organize cultural memory.
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