noun

• A four-year period, particularly (historical) those based on Hippias's computations of the ancient Olympic Games which placed Coroebus's footrace victory in 776 BCE and (sports) those based on the modern Summer Olympic Games first held in 1896.
• (sports, sometimes proscribed) Synonym of Olympic Games: an instance of the ancient or modern Olympic Games.
• (by extension, usually preceded by descriptive words) A competition aspiring to the importance of the Olympic Games or considered similar to them, especially one occurring at 4-year intervals, representing a national or international range of amateur student rather than professional adult competition, and/or requiring the highest level of ability in the field for success.
• Alternative letter-case form of Olympiad, q.v. [A four-year period, particularly (historical) those based on Hippias's computations of the ancient Olympic Games which placed Coroebus's footrace victory in 776 BCE and (sports) those based on the modern Summer Olympic Games first held in 1896.]