submillimeter
adjective
- less than 1 mm in size
Wiktionary
adj
Etymology: * sub- + millimeter
- Less than a millimeter in size.
noun
Etymology: * sub- + millimeter
- A unit or measurement that is less than a millimeter.
“The sizes vary from four to five millimeters, or with laminar resolution functional magnetic resonance imaging (lfMRI), to submillimeters.”