Source : Webster's Revised Unabridged Dictionary (1913)

Olympiad \O*lym"pi*ad\, n.
   The quadrennial celebration of the modern Olympic games; as,
   the first Olympiad (1906).

Olympiad \O*lym"pi*ad\ ([-o]*l[i^]m"p[i^]*[a^]d), n. [L.
   olympias, -adis, Gr. 'olympia`s, -a`dos, fr. 'O`lympos
   Olympus, a mountain in Macedonia: cf. F. olympiade.] (Greek
   Antiq.)
   A period of four years, by which the ancient Greeks reckoned
   time, being the interval from one celebration of the Olympic
   games to another, beginning with the victory of Cor[oe]bus in
   the foot race, which took place in the year 776 b.c.; as, the
   era of the olympiads.

Source : WordNet®

Olympiad
     n 1: one of the 4-year intervals between Olympic Games; used to
          reckon time in ancient Greece for twelve centuries
          beginning in 776 BC
     2: the modern revival of the ancient games held once every 4
        years in a selected country [syn: {Olympic Games}, {Olympics}]