/ Dictionary / Index S submillimeter: Meaning and Definition of Find definitions for: sub•mil•li•me•ter Pronunciation: (sub-mil'u-mē"tur), [key] — adj. less than a millimeter in size: a submillimeter wave. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. submicroscopic subminiature Related Content Daily Word Quiz: neologism Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language