Outside the Christian association, thirty-three has a handful of genuine uses and a great many invented ones.
Freemasonry. The Ancient and Accepted Scottish Rite has thirty-three degrees, the thirty-third being honorary and conferred rather than worked through. The structure was fixed with the founding of the Supreme Council at Charleston in 1801, drawing on earlier French high-degree systems. It is a real institution with a documented history, and the number was an organisational decision of the early nineteenth century, not an inheritance from anywhere older.
Anatomy. A human infant has thirty-three vertebrae; five sacral and four coccygeal fuse in adulthood, leaving twenty-six. The figure is correct, and the use made of it in modern esoteric writing, linking the thirty-three vertebrae to the thirty-three Masonic degrees, to the traditional thirty-three years of the life of Christ, and to the ascent of kundalini, is a twentieth-century construction joining facts that have no historical relation. Manly P. Hall states the linkage directly in The Occult Anatomy of Man (1929), reading the spine as Jacob's Ladder and its vertebra count against both the Scottish Rite and Christ's traditional lifespan; George W. Carey and Inez Eudora Perry's earlier God-Man: The Word Made Flesh (1920) makes the closely related but separately argued claim that the cerebrospinal fluid the vertebrae enclose is itself a Christ-associated substance.
Scripture. 2 Samuel 5:5 gives David thirty-three years reigning in Jerusalem.
Literature. Dante's Commedia gives thirty-three cantos to each of Purgatorio and Paradiso, with thirty-four in Inferno, so the total is a hundred; the arrangement is deliberate and the extra canto is an introduction to the whole poem.
Numerology. Thirty-three is treated as the third master number, after 11 and 22, and given the character of the master teacher. Master numbers are a feature of the twentieth-century American system and are not found in any earlier source; the doctrine surrounding them was largely elaborated after 1930.