Sido - Soma
- Sidon
- Sidonius
- Sidonius Apollinaris
- Sidron de Hossche
- Sidyma
- Siena
- Siena, University of
- Sieni, Cyril
- Sierra Leone
- Sieur de Laverendrye
- Sig.
- Sigebert of Gembloux
- Siger of Brabant
- Sigismond Thalberg
- Sigismund
- Sigismund Albicus
- Sigismund Krasinski
- Sign of the Cross
- Signorelli, Luca
- Sigüenza
- Sikhism
- Silandus
- Silence
- Silesia
- Silesius Angelus
- Siletz Indians
- Siloe
- Silveira
- Silveira, Ven. Goncalo da
- Silverius, Pope Saint
- Silvester Jenks
- Silvester, Francis
- Silvia, Saint
- Silvio Antoniano
- Silvio Pellico
- Simeon
- Simeon of Durham
- Simeon Stylites the Elder, Saint
- Simeon Stylites the Younger, Saint
- Simeon, Canticle of
