cellar-flap, n. — Green’s Dictionary of Slang

cellar-flap n.

[rhy. sl.; the image is of a dance performed on a space no larger than the trap-door leading to a cellar]

a tap-dance; also attrib.

1866		J. Greenwood Little Ragamuffin 319: A hornpipe much in vogue in certain circles [...] and known as the ‘cellar flap.’.
1877		Five Years’ Penal Servitude 219: Others again would indulge in a break-down, or cellar-flap dance, dreadfully to the discomfort of the men in the cells below.
1887		W.S. Gilbert ‘An Unfortunate Likeness’ Fifty ‘Bab’ Ballads 200: Forgive these yells and cellar-flaps.