Resin gathered from the mastic tree. Joseph's brothers (Gen. 37: 25) sold him to merchants whose caravan of camels conveyed this commodity. The reference in Jer. 8: 22 is to a medicinal balm, perhaps the gum of the balsam tree.
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"balm of Gilead." In A Dictionary of the Bible. Ed. W. R. F. Browning. Oxford Biblical Studies Online. Sep 2, 2014. <http://www.oxfordbiblicalcstudies.com/article/opr/t94/e203>.
"balm of Gilead." In A Dictionary of the Bible. , edited by W. R. F. Browning. Oxford Biblical Studies Online, http://www.oxfordbiblicalcstudies.com/article/opr/t94/e203 (accessed Sep 2, 2014).