Source : Webster's Revised Unabridged Dictionary (1913)

Sixty \Six"ty\, a. [AS. siextig; akin to G. sechzig, Goth.
   sa['i]hs tigjus. See {Six}, {Ten}, and cf. {Sixteen}.]
   Six times ten; fifty-nine and one more; threescore.

Sixty \Six"ty\, n.; pl. {Sixties}.
   1. The sum of six times ten; sixty units or objects.

   2. A symbol representing sixty units, as 60, lx., or LX.

Source : WordNet®

sixty
     adj : being ten more than fifty [syn: {60}, {lx}, {threescore}]

sixty
     n : the cardinal number that is the product of ten and six [syn:
          {60}, {LX}]