M
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- Michel-Eugene Chevreul
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- Morality
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- Muri
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- Mush
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- Musti
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- Mylasa
- Myles William Patrick O'Reilly
- Myndus
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- Mystical Marriage
- Mystical Stigmata
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- St. MacCathbad Colman
- St. Machutus
- St. Macrina the Elder
- St. Macrina the Younger
- St. Maelruan
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- St. Margaret
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- St. Margaret of Cortona
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- St. Martha
- St. Martial
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- St. Martin of Tours
- St. Martina
- St. Mary de Cervellione
- St. Mary Frances of the Five Wounds of Jesus
- St. Mary Magdalen
- St. Matilda
- St. Matthew
- St. Matthias
- St. Maurice
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- St. Mechtilde
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- St. Melito
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- St. Mura
- The Machabees
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- The Martyrs of Gorkum
- The Master of Liesborn
- The Maurists
- The Military Orders
- The Monastic School of Aran
- The Monk of Malmesbury