noun the quotient of a unit divided by a thousand; one of a thousand equal parts into which a unit is divided.
2. thousandth ·adj constituting, or being one of, a thousand equal parts into which anything is divided; the tenth of a hundredth.
3. thousandth ·adj 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.
4. thousandth ·adj 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.