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Webster 1913 Edition

(?; 277)

Adj.

[L.

iris

iridis

, rainbow. See

Of or pertaining to the iris or rainbow; prismatic;

as, the

iridal

colors

Whewell.

iridal ‎(comparative more iridal, superlative most iridal)

(rare) Pertaining to a rainbow.
(chiefly medicine) Pertaining to the iris of the eye.
- 1969, Vladimir Nabokov, Ada or Ardor, Penguin 2011, p. 44:
  The iridal dark-brown of her serious eyes had the enigmatic opacity of an Oriental hypnotist's look (in a magazine's back-page advertisement) and seemed to be placed higher that usual so that between its lower rim and the moist lower lid a cradle crescent of white remained when she stared straight at you.