MICRON

One millionth of a metre (6)

Solution has appeared in 2 crosswords (0 across and 2 down):

• Quick crossword No 15,993 — 2021-08-09 23:00:03
  16D: Very small metric unit of length (6)
• Quick crossword No 15,505 — 2020-01-17 00:00:46
  15D: One millionth of a metre (6)