The Collaborative International Dictionary of English v.0.48:

Seventy \Sev"en*ty\, a. [AS. hund-seofontig. See Seven, and
   Ten, and cf. Seventeen, Sixty.]
   Seven times ten; one more than sixty-nine.
   [1913 Webster]

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):

seventy
    adj 1: being ten more than sixty [syn: seventy, 70, lxx]
    n 1: the cardinal number that is the product of ten and seven
         [syn: seventy, 70, LXX]