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[in-som-nee-ak] /ɪnˈsɒm niˌæk/
a person who suffers from insomnia, the inability, especially when chronic, to obtain sufficient sleep, through difficulty in falling or staying asleep:
Her husband, an insomniac, had at last fallen asleep at the computer, head resting on the keyboard.
having insomnia:
a nervous, insomniac person.
of, relating to, or causing insomnia:
long, torturous, insomniac nights.
Origin of insomniac
First recorded in 1905-10; insomni(a) + -ac
Related forms
anti-insomniac, adjective, noun
Word story
Here's your Latin lesson for the day: somnus in Latin means “sleep.” If you tack the prefix “in-” (another Latin word, meaning “not”) onto it, you get a word that means “not sleep.” An insomniac, therefore, is a person who suffers from the inability to sleep.
Once you know the Latin root somn-, which you now do, then you will also recognize it in some related words—somnolent, meaning “sleepy, drowsy,” somniferous, meaning “sleep-inducing,” and somnambulate, meaning “to sleepwalk.”
By now, you can probably guess that a somnambulist is a sleepwalker. Perhaps the most famous somnambulist is Cesare, a carnival attraction in the 1920 silent film The Cabinet of Doctor Caligari.
We hope this story hasn’t been too somniferous—but, if it has, pleasant dreams!
Related Quotations
“The more the insomniac tries to go to sleep, the wider awake he becomes.“
—Andre Muller Weitzenhoffer, The Practice of Hypnotism (2000)
“In the morning she put on her black dress again, and carried her insomniac face proudly to the breakfast table, where Melissy took one look at it and rang up the doctor immediately.“
—Elizabeth Stuart Phelps, “Twenty-Four Four“ Harper’s New Monthly Magazine, Volume 92, Issue 1 (December 1895 to May 1896) Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2018.
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Examples from the Web for insomniac
Historical Examples
  • Most people are insomniac, mainly because they are overanxious about their sleep.

    Psychotherapy James J. Walsh
  • Consciousness came back in little dribbles like a montage—half reality and half nightmare of the insomniac.

    A Woman's Place Mark Irvin Clifton
British Dictionary definitions for insomniac


exhibiting or causing insomnia
a person experiencing insomnia
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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Word Origin and History for insomniac

1877 (adj.); 1879 (n.), from insomnia.

Online Etymology Dictionary, © 2010 Douglas Harper
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insomniac in Medicine

insomniac in·som·ni·ac (ĭn-sŏm'nē-āk')
One who suffers from insomnia. adj.
Having or causing insomnia.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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