Green’s Dictionary of Slang

madza n.

also medza, medzer, midzer
[Ital. mezzo, a half]

1. [mid–late 19C] (Ling. Fr./Polari) a half; thus madza beargured, half-drunk, madza round the bull, half a pound of steak.

2. [late 19C-1920s] a halfpenny.

In compounds

madza caroon (n.) [caroon n.]

[mid–late 19C] half a crown, 2s 6d (12½p).

madza poona (n.) [poona n.]

[mid–late 19C] a half-sovereign.

madza saltee (n.) [saltee n.]

[mid–late 19C] one halfpenny.