1. (a.) Next in order after nine hundred and ninety-nine; coming last of a thousand successive individuals or units; -- the ordinal of thousand; as, the thousandth part of a thing.

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

3. (a.) 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. (n.) The quotient of a unit divided by a thousand; one of a thousand equal parts into which a unit is divided.