Kutscher (pg 28-9) brings up some interesting points about the carob tree - חרוב (haruv/charuv/kharuv). He writes that it appears nowhere in the Bible; this is particularly striking considering there are those that claim that the haruv originated in Eretz Yisrael. He quotes Immanuel Loew as saying that this word is proof that there are words that were used in Biblical times but don't appear in the Tanach, but show up in Tannaic times.
He writes that the etymology of the word is from the sword shaped pod - herev חרב is sword in Hebrew. (Jastrow claims it comes from חרב meaning dry - perhaps due to the dryness of the fruit, or the climate it can grow in). The word passed from Hebrew to Aramaic חרובא, and from Aramaic to Arabic harrubah. In the Middle Ages, it passed from Arabic to the European languages - caroube in French, carruba in Italian and carob in English.
More about other etymologies related to the carob plant (but not the word haruv) tomorrow.