Definition of Nyctophobia

Nyctophobia: Pathological fear of the dark, an abnormal and persistent dread of the dark. Sufferers experience anxiety even though they may rationally realize that the dark does not pose a threat commensurate with their fear.

Formed from the Greek "nyx" (night) and the Greek "phobos" (fear). "Nyx" has also contributed to other medical terms such as "nyctalopia" (night blindness) and "nyctanopia" (impaired vision in dim light and in the dark). Another term for fear of the dark is scotophobia.