The Collaborative International Dictionary of English v.0.48:

Iridescent \Ir`i*des"cent\ (?; 277), a. [L. iris, iridis, the
   rainbow: cf. F. iridescent.]
   Having colors like the rainbow; exhibiting a play of
   changeable colors; nacreous; prismatic; as, iridescent glass.
   See iridescence.
   [1913 Webster]

WordNet (r) 3.0 (2006):

iridescent
    adj 1: varying in color when seen in different lights or from
           different angles; "changeable taffeta"; "chatoyant (or
           shot) silk"; "a dragonfly hovered, vibrating and
           iridescent" [syn: changeable, chatoyant,
           iridescent, shot]
    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 "iridescent":
   burele, chatoyant, creamy, delicate, eggshell, flat, gloss, iridal,
   iridial, iridian, irisated, irised, light, mellow, moire,
   mother-of-pearl, nacre, nacred, nacreous, 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