Flattering nonsense, palaver. In Wales it is a food made of oatmeal steeped in water and kept till it has become sour. In Cheshire and Lancashire it is the prepared skin of oatmeal mixed with honey, ale, or milk; pap; blancmange. (Welsh, llymry, wash-brew, from llym, sour or sharp.)
“You came ... with your red coats and flashing buttons ... and her head got turned with your flummery.” —Simms: The Partizans, chap. xxix.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894