Added 10 October 2026 thirties noun Categories: TimeUncommon Words noun ! Definition from WordNet 3.1, Princeton University. More about thirties at Wordnik → Where our words come from → The time of life between 30 and 40. The decade from 1930 to 1939. Related Words: thirty-somethingmid-thirties1930sonwards30sdepression-era2030s1830sdecadeforties1920s1910s Back to today's word