- (not comparable) Having no brain.
- (comparable) Unintelligent, with little common sense.
- 1907, Robert William Chambers, chapter VI, in The Younger Set, New York, N.Y.: D. Appleton & Company, OCLC 24962326:
- "I don't mean all of your friends—only a small proportion—which, however, connects your circle with that deadly, idle, brainless bunch—the insolent chatterers at the opera, the gorged dowagers, the worn-out, passionless men, the enervated matrons of the summer capital, […]!"
having no brain
unintelligent; having little or no common sense