Etymology

uncanny +‎ valley, calque of Japanese 不気味の谷 ‎(bukimi no tani ぶきみのたに), from Middle Chinese 不 (pjuw "not") + 氣味 (kì-mjɨ̀j "taste and smell", by extension "sense", "sentiment") + Japanese の (no, noun modifier particle) + 谷 ‎(たに tani "valley"). First used in 1970 by roboticist Masahiro Mori.

uncanny valley ‎(uncountable)

1. A range of appearances, mannerisms, and/or behaviors subtly different from humanoid in an otherwise humanoid figure that may cause negative reactions, such as fear, discomfort, or revulsion.
   • 1970, Masahiro Mori, The Uncanny Valley (Energy, 7(4), pp. 33–35):

     So in this case, the appearance is quite human like, but the familiarity is negative. This is the uncanny valley.

   • 2006, Sebastiano Bagnara, Gillian Crampton Smith, Theories and Practice in Interaction Design:

     However, when the robot is so similar that it may be momentarily mistaken for real, the transition has a local minimum characterized by a sudden decrease of familiarity, the "uncanny valley"—a dip of frustration due to unmet expectations.

   • 2007, Jonathon Keats, Control + Alt + Delete: A Dictionary of Cyberslang:

     Almost human in appearance, yet not quite, the characters in 3-D computer animations are more disturbing than overt caricatures. The realm these creatures occupy is called the uncanny valley [...].