ounce, n. — Green’s Dictionary of Slang

ounce n.

[the valuation of silver at five shillings an ounce]

a silver coin.

1725		New Canting Dict.
1823		‘Jon Bee’ Dict. of the Turf, the Ring, the Chase, etc. 131: Ounce so much silver is understood, or five shillings ― same as ‘bull’; ‘I’ll bet ye an ounce of it.’.

twelve ounces in the pound (adj.)

(N.Z.) unstable, eccentric ‘not all there’.

1953

I. Hamilton Till Human Voices Wake Us 177: You and hot-headed? [...] Twelve ounces in the pound, you mean, don’t you.