The Collaborative International Dictionary of English v.0.48:

Seventy \Sev"en*ty\, n.; pl. Seventies.
   1. The sum of seven times ten; seventy units or objects.
      [1913 Webster]

   2. A symbol representing seventy units, as 70, or lxx.
      [1913 Webster]

   The Seventy, the translators of the Greek version of the
      Old Testament called the Septuagint. See Septuagint.
      [1913 Webster]

WordNet (r) 3.0 (2006):

seventies
    n 1: the decade from 1970 to 1979 [syn: seventies, 1970s]
    2: the time of life between 70 and 80 [syn: seventies, mid-
       seventies]