Note 2628 — BOOK IX. THE NATURAL HISTORY OF FISHES.
John Bostock translation
Isidorus and Solinus, however, say that the pearl is so called, because two are never found together. The derivation given by Pliny is, however, the more probable one. From the Latin “unio,” comes our word “onion;” which, like the pearl, consists of numerous coats, one laid upon the other.