"having variegated and changing colors like those of an opal," 1810, from opal + -escent. Perhaps via French opalescent.
a milky opalescent (or opaline) luster
op. cit.
opacity
opafication
opal
opalescence
opalescent
opaque
ope
OPEC
op-ed
open
)window.location='https://www.paypal.com/cgi-bin/webscr?cmd=_donations&business=byronic106@yahoo.com&lc=US&item_name=Donation+to +Help+Keep+Etymonline+Free+and+Open&no_note=0&cn=&curency_code=USD&bn=PP-DonationsBF:btn_donateCC_LG.gif:NonHosted'){kind=link}