The Nuttall Encyclopedia
A tree, according to Moslem belief, growing in hell, and of the bitter fruit of which the damned are compelled to eat so as to intensify their torment.
Wood, James, ed. Entry for 'Zakkum'. The Nuttall Encyclopedia. https://www.studylight.org/encyclopedias/eng/nut/z/zakkum.html. Frederick Warne & Co Ltd. London. 1900.