Definition of "finnuf"

Them that puts the most steam into it will get a finnuf slipped to 'em.

1927, Irvin Shrewsbury Cobb, Ladies and Gentlemen, page 129

"Ya-ar, she's rich, ain't she? Wotjer think? I lay they got a 'aul! Sixty bob, may be. And crowns! And finnufs! Ar!"

1949, Theodore Bonnet, The Mudlark, page 216