millesimal

1. Thousandth.
2. Consisting of a thousandth.
3. Relating to thousandths.

[From Latin mīllēsimus, from mīlle, thousand.]

With divisor/multiplier steps of 1 000, in contrast with the steps of 10 for decimal, of 100 for centesimal.

The SI system, although basically decimal through its metric heritage, is largely millesimal. Official policy is for scaling beyond a factor of 100 to be effected in steps of 10³ and, while the prefixes for 10 and 100 multiplication and division are retained, they are not universally legal for commerce.

Steps of 1 000 have the advantage of minimizing the scope for confusion of the unit involved, e.g. on architectural drawings.