a. Lacking intelligence; stupid or empty-headed.
b. Devoid of substance or meaning; vapid or inane: a vacuous comment.
c. Devoid of expression; vacant: a vacuous stare. See Synonyms at empty.
2. Lacking serious purpose or occupation; idle: "A sleepless night was followed by a vacuous day" (Zon Ferraris).
3. Archaic Devoid of matter; empty: vacuous space.
[From Latin vacuus, empty; see VACUUM.]
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2020 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.