"nacreous mass formed in the shell of a bivalve mollusk as a result of irritation caused by some foreign body," early 14c., perle (mid-13c. as a surname), from Old French perle (13c.) and directly from Medieval Latin perla (mid-13c.), which is of unknown origin. Perhaps from Vulgar Latin *pernula, diminutive of Latin perna, which in Sicily meant "pearl," earlier "sea-mussel," literally "ham, haunch, gammon," so called for the shape of the mollusk shells.
Used from 14c. of anything valuable or of the finest kind; from mid-15c. of something small, round, and glistening white. For pearls before swine, see swine. Pearl Harbor translates Hawaiian Wai Momi, literally "pearl waters," so named for the pearl oysters found there; transferred sense of "effective sudden attack" is attested from 1942 (in reference to Dec. 7, 1941).
late 14c., "to adorn with pearls," from pearl (n.). From 1590s as "to take a rounded form" (intrans.); from c. 1600 as "to make into a form, or cause to assume the form and appearance, of a pearl" (trans.). Related: Pearled; pearling.