Green’s Dictionary of Slang

1. (Aus., also halfy) a half-caste.

1941		Argus (Melbourne) 15 Nov. (Supplement) 1/3: Slang applied to the aborigines occurs, of course, only in the Far North [...] They are referred to invariably as ‘Boongs’. Half-castes are ‘halfies’, and quartercastes ‘creamies’ .
1955		N. Pulliam I Travelled a Lonely Land (1957) 233/2: halfy (halfie) a half-caste.
1960		J. Walker No Sunlight Singing (1966) 195: Say, Les, what’s the drill with these halfies? [...] That dance I went to th’ other night. There was all colours there – black, white, brown and brindle.
1984		Partridge DSUE (8th edn) 523: since ca. 1910.

2. a half-brick.

1998

K. Sampson Awaydays 16: Bottles and halfies raining down from the Wrexham end.

3. see half n. (6)