[ in-som-nee-ak ]
See synonyms for insomniac on
  1. a person who has or experiences 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.

  1. having insomnia: a nervous, insomniac person.

  2. of, relating to, or causing insomnia: long, torturous, insomniac nights.

Origin of insomniac

First recorded in 1905–10; insomni(a) + -ac

word story For insomniac

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!

Other words for insomniac

Other words from insomniac

  • an·ti-in·som·ni·ac, adjective, noun

Words Nearby insomniac Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

How to use insomniac in a sentence

  • 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


/ (ɪnˈsɒmnɪˌæk) /

  1. exhibiting or causing insomnia

  1. 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