Green’s Dictionary of Slang

(US) magnificent, splendid, large; thus magnoliousness, the fact or quality of being magnolious.

1865		G.A. Sala My Diary in America 114: But..she might be the sheriff’s daughter..., accustomed to go out on Sundays with a ‘magnolious’ parasol and a ‘spanglorious’ crinoline.
1913		DN IV 19: Magnolious, very fine, magnificent. Used in Wyoming. ‘How do you like my suit?’ ‘It’s magnolious.’.
1922		S. Lewis Babbitt (1974) 260: Come now, Lady Wycombe, if you’ll take the Duke of Zenith’s arm, we will proambulate in to the magnolious feed!
1942		Wake Forest College Alumni News Dec. 🌐 The man of the hour was Dr. Tom Jeffries, scholar, thinker, preacher, and floriculturist, who made by far the most magnolious talk of the many magnolious ones he had delivered in honor of the occasion.
1950		J.T. McCutcheon Drawn from Memory 346: Never before or since has the Island seen such a magnolious night.
1978		F. Pohl Way the Future Was 85: John swallowed whole such magnolious nonsense as dianetics, the Hieronymous machine, and the John Birch Society.
1999		F. Pohl Far Shore of Time (2000) 220: Filling myself full of magnolious notions of coming back a hero to save the world.