Source : Webster's Revised Unabridged Dictionary (1913)

Sixtieth \Six"ti*eth\, a. [As. sixtiogo[eth]a, sixtigo[eth]a.]
   1. Next in order after the fifty-ninth.

   2. Constituting or being one one of sixty equal parts into
      which anything is divided.

Sixtieth \Six"ti*eth\, n.
   1. The quotient of a unit divided by sixty; one of sixty
      equal parts forming a whole.

   2. The next in order after the fifty-ninth; the tenth after
      the fiftieth.

Source : WordNet®

sixtieth
     adj : the ordinal number of sixty in counting order [syn: {60th}]
     n 1: position 60 in a countable series of things
     2: one part in sixty [syn: {one-sixtieth}]