The Collaborative International Dictionary of English v.0.48:

Nacreous \Na"cre*ous\ (n[=a]"kr[-e]*[u^]s), a. [See Nacre.]
   (Zool.)
   Consisting of, or resembling, nacre; pearly.
   [1913 Webster] Nad

WordNet (r) 3.0 (2006):

nacreous
    adj 1: consisting of or resembling mother-of-pearl
    2: having a play of lustrous rainbow colors; "an iridescent oil
       slick"; "nacreous (or pearlescent) clouds looking like
       mother-of-pearl"; "a milky opalescent (or opaline) luster"
       [syn: iridescent, nacreous, opalescent, opaline,
       pearlescent]

Moby Thesaurus II by Grady Ward, 1.0:

48 Moby Thesaurus words for "nacreous":
   burele, chatoyant, creamy, delicate, eggshell, flat, gloss, iridal,
   iridescent, iridial, iridian, irisated, irised, light, mellow,
   moire, mother-of-pearl, nacre, nacred, nacry, opalescent, opaline,
   opaloid, pale, pastel, patinaed, pavonian, pavonine, pearl-like,
   pearlish, pearly, quiet, rainbowlike, rainbowy, sad, semigloss,
   simple, sober, soft, soft-colored, soft-hued, softened, somber,
   subdued, subtle, sweet, tender, tortoise-shell