(1):
(a.) Constituting, or being one of, a thousand equal parts into which anything is divided; the tenth of a hundredth.
(2):
(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.
(3):
(a.) 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.
(4):
(n.) The quotient of a unit divided by a thousand; one of a thousand equal parts into which a unit is divided.