Adjective
submicroscopic (not comparable)
Smaller than microscopic; too small to be seen even with a microscope
In general semantics, it is always possible to give a description of empirical facts, but such descriptions remain just that—descriptions—which necessarily leave out many aspects of the objective, microscopic, and submicroscopic events they describe. Source: Internet
For Virology is the study of viruses – submicroscopic, parasitic particles of genetic material contained in a protein coat citation citation – and virus-like agents. Source: Internet