See Classical Latin paederos (Lewis and Short 1288c), from Byzantine Greek παιδέρως. As used in Pliny the word refers to a type of precious stone which can be interpreted as either opal or amethyst. The single Anglo-Norman citation uses a plural lexeme, but treats it as a singular form. The word appears in English from the sixteenth century. See OED peridot n., TLF péridot and FEW pierres précieuses (21,42b) for the suggestion that the etymon, through metathesis, produced the more common peridout.