/ Dictionary / Index A aplanatic: Meaning and Definition of Find definitions for: ap•la•nat•ic Pronunciation: (ap"lu-nat'ik), [key] — adj. Optics. free from spherical aberration and coma. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: aplanatic (Thesaurus) aplacophoran aplanetic Related Content Daily Word Quiz: respite Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language