The word 'decade' refers to-

Correct Answer: (C) ten years Knowledge of time-period words is an important vocabulary area in NTRCA exams. "Decade" — Definition: — A decade = a period of 10 years — Etymology: from Latin "decas" and Greek "dekas" meaning "a group of ten" — Example: "In the last decade, technology has advanced rapidly." Time-Period Vocabulary Chart (Must Memorize): — Decade = 10 years — Score = 20 years — Quarter century = 25 years — Generation = approximately 30 years — Jubilee = 50 years — Century = 100 years — Millennium = 1,000 years — Lustrum = 5 years — Fortnight = 14 days (2 weeks) — Biennial = every 2 years — Triennial = every 3 years — Quinquennial = every 5 years — Centennial/Centenary = 100 years anniversary Why others are wrong: ✗ Thirty years — not a standard English time-period term ✗ Fifty years — that would be "jubilee" or "half-century" ✗ Twenty-five years — that is a "quarter century" or "silver jubilee" Source: Oxford English Dictionary; Vocabulary for Competitive Exams; NTRCA Question Bank.