First signs of near miss might indicate such a small distance (9)
I believe the answer is:
nanometre
'small distance' is the definition.
(a nanometre is a very small distance)
I can't explain the rest of the clue.
(Other definitions for nanometre that I've seen before include "tiny distance" , "Some tiny measure" , "small unit" , "A very small length" , "Very, very short length" .)