flummadiddle, n. — Green’s Dictionary of Slang

flummadiddle n.

also flummerdiddle, flummydiddle, fumadiddle

[? SE flummery, nonsense + diddle n.³; Flummery was also a variety of sweet dish; thus note flummadiddle, ‘stale bread, pork-fat, molasses, cinnamon, allspice, from which a kind of mush is made, which is baked in the oven and brought to the table hot and brown’ (Schele de Vere, Americanisms, 1872)]

(US)

1. nonsense, empty flattery, humbug; also as adj.

1854		M.J. Holmes Tempest and Sunshine 21: What does she want of any more flummerdiddle notions?
1868		G.E. Brackett Farm Talk 70: What’s the use of so much ‘flummy-diddle’? Plain common sense is enough for any farmer’s paper.
1882		Century mag. (N.Y.) Oct. 837: Well, see all that flummer-diddle he got off about it.
1919		O.R. Cohen ‘Pool and Genuwine’ in Polished Ebony 54: ‘I ain’t calculatin’ no fumadiddle from you nor no other man’.
1989		H. Rawson Dict. of Invective (1991) 33: A variant, with both culinary and nonsense meanings, is flummadiddle.

2. something trivial or ridiculous.

1903

G.D. Chase ‘Cape Cod Dialect’ in DN II:v 297: flummydiddle, n. Foolishness.