October 21 (Eastern Orthodox liturgics)

• Hieromartyr Socrates, Priest, and Martyr Theodote, of Ancyra (c. 230)[1][2][3][note 2]
• Martyrs Dasius, Gaius, and Zoticus at Nicomedia (303)[1][3][4][5][note 3]
• Saint Darius, Zosimus, Paul, and Secundus, martyrs of Nicaea by Diocletian (4th century)[7]
• Martyr Azes, by fire.[3][8][9][10]
• Saints Plantinos (Platinus), Irene and Marina of Raithu.[3][9][11][note 4]
• Venerable Hilarion the Great, of Gaza (371)[1][3][10][12][13][14][note 5]
• The 63 Martyrs of Jerusalem (724):[1][15]

• Pegasus, Neophytus, Acacius, Dorotheus, Stephen, Dometius, Herman, Dionysius, Epiphanius, Stratonicus, Leontius, Emmanuel, Theophilus, Elias, John, Samuel, Eulampius, Alexius, Photius, Eutrepius, Methodius, Chariton, Theophylactus, Anastasius, Andronicus, Symeon, Theoktistus, Romanus, Paul, Agathonicus, Minas, Athanasius, Jacob, Nicephorus, Porphyrius, Timothy, Irenarchus, Auxentius, Joseph, Gregory, Callinicus, Aaron, Cyriacus, Theodosius, Eustathius, Isaac, Alexander, Eleutherius, Adrian, Christophor, Antiochus, Isidore, Parthenius, Sergius, Euplus, Ignatius, Theophanes, Cyril, Zachariah, and Anthimus.

• Martyrs Andrew, Stephen, Paul and Peter, under Constantine V Copronymus (c. 741-775)[3][9][10][16][note 6]
• Venerable martyr Zacharias, by drowning in the sea.[3][9][10][17]
• Venerable Baruch, reposed in peace.[3][9][10][18]
• Venerable Phillip.[9][19]
• Venerable Jacob, Oeconomus of Batheos Rhyakos Monastery.[3][9][20][note 7]

• Saint Asterius of Ostia, martyred priest (c. 223)[21][22][note 8][note 9]
• Saint Viator of Lyons, hermit (389).[21][note 10][note 11]
• Saint Ursula of Cologne and her companions, martyrs at Cologne (c. 451)[1][9][10][21][23][24][25][note 12][note 13]
• Saint Cilinia, the mother of St Principius, Bishop of Soissons and St Remigius, Bishop of Rheims (c. 458)[21][note 14]
• Saint Fintan Munnu (Finian), of Teachmunnu, Ireland (635)[1][9][10][21][26][27][note 15]
• Saint Tuda of Lindisfarne, Bishop of Lindisfarne (c. 664)[21][note 16]
• Saint Condedus (Condé, Condède), a hermit at Fontaine-de-Saint-Valéry in the north of France (c. 690)[10][21][note 17]
• Saint Wendelin of Trier (Wendolinus, Wendel), a shepherd who was famous for his holiness and is venerated at St Wendel on the Nahe in the west of Germany (7th century)[21][note 18]
• Saint Malathgen of Cluain-Edneach, Ireland, Abbot (767)[1][10]
• Saint Hugh of Ambronay, third Abbot of Ambronay Abbey near Belley in France (9th-10th centuries)[21]
• Saint Maurontus, Abbot of St Victor at Marseilles, he became bishop of the same city around 767 (c. 804)[21]

• Saint Hilarion of Kiev, the first non-Greek Metropolitan of Kiev (c. 1055)[1][9][10][29]
• Venerable Hilarion the Schemamonk of the Kiev Caves (11th century)[1][3][9][10][30][31][32]
• Venerables Barnabas and Hilarion the Wonderworkers, of Peristerona, Cyprus, of the "300 Allemagne Saints" in Cyprus (12th century)[3][9][33][note 19]
• Venerable Philotheus of Neapolis and Mt. Athos (14th century)[1][3][10][36][37]
• Saints Theophilus and James, monks of Konevits, founders of Dormition Monastery at Omutch (modern-day Feofilova Pustyn'),^(ru) Pskov (c. 1412)[1][10][30][38]
• Saint Hilarion, founder of Pskovoezersk Monastery, Gdov (1476)[1][10][30][39][40][note 20]
• Saints Bessarion (Sarai), Hieromonk (1745),[41][note 21] and Sophronius of Ciorara, monk (c. 1765),[42][note 22] Confessors, and St. Oprea of Săliște (18th century),[43] martyred by the Latins in Romania.[1][10]
• New Martyr John of Monemvasia, Peloponnesus, at Larissa (1773)[1][3][9][10][44]
• Hiero-confessors John of Galёs,[45][note 23] and Moses (Macinic),[46] Priests, of Sibiel, Transylvania (18th century)[1][10]

• Translation of the relics of St. Christodoulos the Wonderworker of Patmos (1093)[1][3][9][10][59][note 30]
• Translation of the relics (1206) of St. Hilarion, Bishop of Meglin, Bulgaria (1164)[1][9][10][30][60][61]
• Repose of Schema-Archimandrite Herman (Bogdanov) of New Valaam Monastery in Siberia (1938)[1]
• Repose of Schema-Nun Seraphima (Bobkova) of Shamordino Convent (1990)[1]

• 
  Venerable Hilarion the Great.
• 
  Martyrs Dasius, Gaius, and Zoticus, at Nicomedia.
• 
  St. Ursula of Cologne
• 
  Saint Cilinia of Laon.
• 
  St. Wendelin of Trier.
• 
  Saint Hilarion of Kiev, Metropolitan of Kiev.
• 
  Sts. Bessarion (Sarai) and Sophronius of Ciorara, Confessors, and St. Oprea of Săliște.
• 
  New Hieromartyr Alexis (Bui), Bishop of Voronezh.
• 
  New Hieromartyr Paulinus (Kroshechkin), Archbishop of Mogilev.
• 
  New Hieromartyr Arcadius (Yershov), Bishop of Ekaterinburg.
• 
  New Hieromartyr Damian (Voskresensky), Archbishop of Kursk.

• October 21 / November 3. Orthodox Calendar (PRAVOSLAVIE.RU).
• November 3 / October 21. HOLY TRINITY RUSSIAN ORTHODOX CHURCH (A parish of the Patriarchate of Moscow).
• October 21. OCA - The Lives of the Saints.
• The Autonomous Orthodox Metropolia of Western Europe and the Americas (ROCOR). St. Hilarion Calendar of Saints for the year of our Lord 2004. St. Hilarion Press (Austin, TX). p. 78.
• The Twenty-First Day of the Month of October. Orthodoxy in China.
• October 21. Latin Saints of the Orthodox Patriarchate of Rome.
• The Roman Martyrology. Transl. by the Archbishop of Baltimore. Last Edition, According to the Copy Printed at Rome in 1914. Revised Edition, with the Imprimatur of His Eminence Cardinal Gibbons. Baltimore: John Murphy Company, 1916. p. 325.
• Rev. Richard Stanton. A Menology of England and Wales, or, Brief Memorials of the Ancient British and English Saints Arranged According to the Calendar, Together with the Martyrs of the 16th and 17th Centuries. London: Burns & Oates, 1892. pp. 508–510.

Greek Sources

• Great Synaxaristes: (in Greek) 21 ΟΚΤΩΒΡΙΟΥ. ΜΕΓΑΣ ΣΥΝΑΞΑΡΙΣΤΗΣ.
• (in Greek) Συναξαριστής. 21 Οκτωβρίου. ECCLESIA.GR. (H ΕΚΚΛΗΣΙΑ ΤΗΣ ΕΛΛΑΔΟΣ).
• (in Greek) 21/10/2017. Ορθόδοξος Συναξαριστής.

Russian Sources

• (in Russian) 3 ноября (21 октября). Православная Энциклопедия под редакцией Патриарха Московского и всея Руси Кирилла (электронная версия). (Orthodox Encyclopedia - Pravenc.ru).
• (in Russian) 21 октября по старому стилю / 3 ноября по новому стилю. Русская Православная Церковь - Православный церковный календарь на 2016 год.