[ 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 formsan·ti-in·som·ni·ac, adjective, noun
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)

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!

Popular references

Insomniac: An album by the punk band Green Day, released in 1995.
Insomniac with Dave Attell: A Comedy Central television show, hosted by Dave Attell, which ran in the early 2000s. Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for insomniac

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

    A Woman's Place|Mark Irvin Clifton
  • Most people are insomniac, mainly because they are overanxious about their sleep.

    Psychotherapy|James J. Walsh

British Dictionary definitions for insomniac


/ (ɪnˈsɒmnɪˌæk) /


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

Word Origin and History for insomniac


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

Online Etymology Dictionary, © 2010 Douglas Harper

Medicine definitions for insomniac


[ ĭn-sŏmnē-ăk′ ]


One who suffers from insomnia.


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