decadedecade

Decade comes from Old French decade, from Late Latin decās ‘set of ten’, from Ancient Greek δεκάς, from δέκα ‘ten’, ultimately from Proto-Indo-European *déḱm̥.

1. Proto-Indo-Europeanc. 4500–2500 BCE*déḱm̥¹‘ten’reconstructed
2. Proto-Hellenicc. 2200–1600 BCE*dékə¹‘ten’reconstructed
3. Ancient Greekc. 800–300 BCEδέκα²déka‘ten’
4. Ancient Greekc. 800–300 BCEδεκάς²dekás‘the number ten’
5. Late Latinc. 200–600 CEdecās²‘(set of) ten’
6. Old Frenchc. 842–1400decade²
7. Middle Englishc. 1150–1500decade²
8. Englishearliest quotation 1979decade²

1. ¹ Wiktionary, Ancient Greek δέκα
2. ² Wiktionary, English decade
3. Earliest quotation in Wiktionary’s entry: 1979, Museums: “Thru May: 1920s — The Decade That Roared. New…”.