Nacreous \NEY-kree-uhs\ , adjective;
1. Resembling nacre (mother-of-pearl); lustrous; pearly
This word is so boring, I can't believe I'm even bothering to tell you what the etymology dictionary says:
From 1840, it means "resembling nacre" from nacre + -ous.
At least the nacre is slightly more interesting. According to Etymonline.com:
The word nacre dates to the 1590's and comes from Middle French meaning "type of shellfish that yields mother-of-pearl." The word probably entered the Romance language family via Italian from Arabic as naccaro (now nacchera). The Arabic word is nakara, meaning "to hollow out," in reference to the shape of the mollusk shell. The association between nacre and mother-of-pearl started around 1718.
*Today's word and the first definition were both taken from Dictionary.com's 'Word of the Day' for Saturday, November 6