Diamond is another of those words that English and Armenian languages share due to some common source. More than two thousand years ago, the Latin word adamantem meant “the hardest metal,” and then it was used to mean our well-known diamond. Then Old French borrowed from Medieval Latin (diamantem) and turned it into diamant. In the early fourteenth century, the word entered English as diamond.
Actually, the Romans had borrowed the word from Greek: ἀδάμας (adámas “unbreakable,” with ἀ meaning “un” and δάμας “conquer, overpower”). The Armenians did the same: the word ադամանդ (adamand; Western Armenian atamant) already appeared in the Bible with the meaning of the precious stone.
Incidentally, the format of the Armenian word is very close to English adamant, whose meaning comes directly from the Greek meaning “unbreakable,” via Latin and French. While the English language created two words from the same original source, the Armenian language simply used atamant and, at times, gave it a metaphoric meaning. For instance, St. Gregory of Narek used the expressions atamantea sird (ադամանդեայ սիրտ “diamond heart”) or atamantea havadk (ադամանդեայ հաւատք “diamond faith”) to mean that the heart or the faith can be as unbreakable as a diamond.