Catechism of the Catholic Church §188 — excerpt
The Greek word symbolon meant half of a broken object, for example, a seal presented as a token of recognition. the broken parts were placed together to verify the bearer's identity.
This translation is under copyright, so only the cited words are quoted here. Follow the link for the full text. Translation: English translation of the Catechism of the Catholic Church, 2nd ed. (Libreria Editrice Vaticana), as posted at vatican.va.