Source : Webster's Revised Unabridged Dictionary (1913)

Seventieth \Sev"en*ti*eth\, a. [AS. hund-seofontigo[eth]a.]
   1. Next in order after the sixty-ninth; as, a man in the
      seventieth year of his age.

   2. Constituting or being one of seventy equal parts.

Seventieth \Sev"en*ti*eth\, n.
   1. One next in order after the sixty-ninth.

   2. The quotient of a unit divided by seventy; one of seventy
      equal parts or fractions.

Source : WordNet®

seventieth
     adj : the ordinal number of seventy in counting order [syn: {70th}]
     n : position 70 in a countable series of things