Definition of "yennep"

To discover the kind of entertainment, a lad near me and my companion was asked "if there was any flash dancing." With a knowing wink the boy answered "Lots! show their legs and all, prime!" and immediately the boy followed up this information by a request for a "yennep" to get a "tib of occabot."

1851, Henry Mayhew, London Labour and the London Poor, volume 1, Of the "Penny Gaff", page 41

Now what are you two squabblin' over? Oh! Jack's got a yennep, and Jim's iookin' shirty.

1882, George MacDonald, “If I Had a Father”, in Stephen Archer and Other Strange Tales, act 2

"Give me two gen, then, and take the whole bloody tol. I've walked me teef orf afore rouf this mornin', and wot 'ave I got? Two bloody yenneps! I ask yer."

1978, Rose Ayers, The Street Sparrows