SYN: submicroscopic.
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1) too small to be seen with an ordinary microscope compare MACROSCOPIC, MICROSCOPIC (2), SUBMICROSCOPIC
2) of or relating to an ultramicroscope
ul·tra·mi·cro·scop·i·cal·ly -i-k(ə-)lē adv
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ul·tra·mi·cro·scop·ic (ul″trə-mi″kro-skopґik) 1. pertaining to the ultramicroscope. 2. too small to be seen with an ordinary microscope.Medical dictionary. 2011.