Source : Webster's Revised Unabridged Dictionary (1913)

Thousandth \Thou"sandth\, n.
   The quotient of a unit divided by a thousand; one of a
   thousand equal parts into which a unit is divided.

Thousandth \Thou"sandth\, a.
   1. Next in order after nine hundred and ninty-nine; coming
      last of a thousand successive individuals or units; -- the
      ordinal of thousand; as, the thousandth part of a thing.

   2. Constituting, or being one of, a thousand equal parts into
      which anything is divided; the tenth of a hundredth.

   3. Occurring as being one of, or the last one of, a very
      great number; very small; minute; -- used hyperbolically;
      as, to do a thing for the thousandth time.

Source : WordNet®

thousandth
     adj : the ordinal number of one thousand in counting order [syn: {1000th}]
     n 1: position 1,000 in a countable series of things
     2: one part in a thousand [syn: {one-thousandth}]