brainless

From Middle English braynles; equivalent to brain +‎ -less.

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brainless (comparative more brainless, superlative most brainless)

1. (not comparable) Having no brain.

   Synonym: anencephalous

   • 1912, Arthur Conan Doyle, The Lost World […], London, New York, N.Y.: Hodder and Stoughton, →OCLC:

     Surely it was more likely that a brainless creature, acting solely by vague predatory instinct, would give up the chase when I disappeared, and, after a pause of astonishment, would wander away in search of some other prey?

2. (comparable) Unintelligent, with little common sense.
   • 1907 August, Robert W[illiam] Chambers, chapter VI, in The Younger Set, New York, N.Y.: D. Appleton & Company, →OCLC:

     "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, […]!"

• bairnless