Crossword Genius

So slight as to remain undetected by the senses (13)

Ross

I believe the answer is:

imperceptible

(Other definitions for imperceptible that I've seen before include "Not discernible by the senses" , "Unnoticeable" , "Too slight to be noticed" , "Too small to be noticed" , "Barely detectable" .)

I've seen this clue in The Times.
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