from The American Heritage® Dictionary of the English Language, 4th Edition

  • n. See night blindness.

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • n. The inability to see clearly in dim light; night blindness

from the GNU version of the Collaborative International Dictionary of English

  • n. A disease of the eye, in consequence of which the patient can see well in a faint light or at twilight, but is unable to see during the day or in a strong light; day blindness.
  • n. See moonblink.

from The Century Dictionary and Cyclopedia

  • n. Night-blindness.
  • n. Day-blindness.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • n. inability to see clearly in dim light; due to a deficiency of vitamin A or to a retinal disorder


Late Latin nyctalōpia, from Greek nuktalōps, night-blind : nux, nukt-, night; see nekw-t- in Indo-European roots + alaos, blind + ōps, ōp-, eye; see okw- in Indo-European roots.
(American Heritage® Dictionary of the English Language, Fourth Edition)



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  • Today's Word of the Day is a seriously conflicted item. The definitions and examples provided support its use to mean
    1. night blindness
    2. day blindness
    3. especially keen vision in low light
    The OED confirms this multiplicity of uses, including among its examples the following:
    "1684 tr. S. Blankaart Physical Dict. 208 Nyctalopia is two-fold: the first is a Dimness of Sight in the Night..: The other is a Dimness in the Light, and clear Sight in the Night, or in Shades."
    To add to the confusion see the definition offered by The Century for hemeralopia:
    "n. In pathology, a defect of sight in consequence of which distinct vision is possible only in artificial or dim light; day-blindness. The term is also used, however, to express exactly the opposite defect of vision. See nyctalopia."
    Versatility is a useful quality in many things but not so much in words.

    Also, all the links to the Jules Verne novel “In Search of the Castaways” in the usage examples fail. Here is a working link to the book at the Gutenberg Project:

    Low clouds the sun's set alight
    I saw once as dawn growing bright.
    As grim nyctalopia
    Turns everything taupier
    I now see the falling of night.

    March 25, 2016