The American Church Dictionary and Cycopedia
The first Sunday after Easter is the Octave of the Queen of Festivals and is commonly called "Low Sunday." It is so called from its contrast with the High Festival of Easter Day. The same note of holy joy is struck, but lower down on the scale.
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Miller, William James. Entry for 'Low Sunday'. The American Church Dictionary and Cyclopedia. https://www.studylight.org/dictionaries/eng/acd/l/low-sunday.html. 1901.