Green’s Dictionary of Slang

waterloo n.¹

a halfpenny.

1909

J. Ware Passing Eng. of the Victorian Era 259/2: Waterloo (Streets, 16 cent. to about 1870). Half-penny – as thus. There was a half-penny toll over Waterloo Bridge, on the Surrey side of which lived most of the poorer common women who harassed the Strand.