Definitions:

1. Relating ot or observable only with an untramicroscope or more advanced instruments like an electron microscope. ADJECTIVE
   • Researchers used electron microscopy to examine the ultramicroscopic structure of the material.
2. Too small to be seen with a standard light microscope. ADJECTIVE
   • The virus particles are ultramicroscopic, invisible even under a regular microscope.

Synonyms:

• infinitesimal
• nanoscopic
• submicroscopic