If you still use a pencil to write, then you probably have an eraser around to rub out pencil marks. Because of such use, the elastic substance that came from tropical plants has been called rubber since the end of the eighteenth century.
Something similar happened in Armenian: the elastic substance was called redeen (ռետին) and your eraser bears the same name redeen. Unlike English, however, the word had no relation with the function of the eraser, but was created from a different source. It was the name of a substance that flowed from trees as a balsam or a medicine. Armenian medical books from the Middle Ages advised: “Redeen, which is a balsam.”
The word redeen probably entered the Armenian language through the translation of the Bible in the fifth century, and its source was the Greek word rhetine “pine resin.” Several other languages borrowed this word: Latin resina, Arabic ratinag, Farsi ratiyan.
Of course, the Latin word sounds familiar. It is the indirect source, through Old French, for the current English word resin.
But where does the Greek word, the common ancestor for Armenian redeen and English resin, come from? That is one of the many mysteries that students of the language have not been able to solve so far.