Webster's Revised Unabridged Dictionary · 1913

Microscopic

Microscopic , adjective

[Compare French microscopique.]

1.
Of or pertaining to the microscope or to microscopy; made with a microscope; as, microscopic observation.
2.
Able to see extremely minute objects.
Why has not man a microscopic eye? — Pope
3.
Very small.
visible only by the aid of a microscope; as, a microscopic insect; also used figuratively; as, a microscopic advantage.

Also: Microscopical