"O most holy" is a Roman Catholic hymn, an old ode in Latin to the Virgin Mary : "O sanctissima, o purissima (piissima), dulcis virgo Maria" and sung in various languages on her feast days. The earliest known publication was from London in 1785 presenting it as a traditional song from Sicily, but no original source or date has been confirmed for the simple melody or the poetic text. The work is often called "Sicilian Mariners Hymn"