Unit of length equal to one thousandth of a millimetre (6)

I believe the answer is:

micron

(Other definitions for micron that I've seen before include "One millionth of 3 Across" , "Small length" , "One-millionth of a metre" , "Micrometre" , "One millionth of 1 metre" .)

I've seen this clue in The Independent.

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