The Nuttall Encyclopedia
A small coin worth about a penny, according to a custom among the Greeks placed in the mouth of a corpse at burial to pay to Charon to ferry the ghost of it over the Styx.
Wood, James, ed. Entry for 'Obelus'. The Nuttall Encyclopedia. https://www.studylight.org/encyclopedias/eng/nut/o/obelus.html. Frederick Warne & Co Ltd. London. 1900.