Source : Webster's Revised Unabridged Dictionary (1913)

Opalescent \O`pal*es"cent\, a.
   Reflecting a milky or pearly light from the interior; having
   an opaline play of colors.

Source : WordNet®

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