nacreous (adj.)

1590s, "type of shellfish that yields mother-of-pearl," from French nacre (Old French nacaire, 14c.), from Italian naccaro (now nacchera), possibly from Arabic naqur "hunting horn" (from nakara "to hollow out"), in reference to the shape of the mollusk shell. Meaning "mother-of-pearl" is from 1718. The French adjectival form nacré was applied in English to decorative objects iridescent like mother of pearl (1895).

word-forming element making adjectives from nouns, meaning "having, full of, having to do with, doing, inclined to," from Old French -ous, -eux, from Latin -osus (compare -ose (1)). In chemistry, "having a lower valence than forms expressed in -ic."