ostracon

/ˈɒstɹəˌkɒn/

IPA: /AO1 S T R AH0 K AH0 N/

noun
  1. 1

    A piece of pottery or stone, usually broken off from a vase or other earthenware vessel, especially one used to cast a vote during the Ancient Greek process of ostracism.

Source: https://en.wiktionary.org/wiki/ostracon