The decade of the 1940s, or a person's age from 40 to 49 years old. Can also refer to the temperature range from 40 to 49 degrees.
From 'forty' (Old English 'feowertig'), literally meaning 'four tens'. The plural form developed to describe decades (1840s, 1940s, etc.) and age ranges, becoming common in the 19th and 20th centuries as standardized ways to discuss time periods and life stages.
The 1940s were perhaps the most globally transformative decade in human history, encompassing World War II, the Holocaust, the atomic age, and the beginning of the Cold War. When people say 'the forties,' they're usually referring to this pivotal decade rather than any other century's version.
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