Green’s Dictionary of Slang

(Aus.) the face or head.

1885		Bulletin (Sydney) 9 May 22/2: The General of the Kopnobrims, having received half a fossilized loaf plump on the ‘ponum,’ hastily ordered an advance along the whole line.
1890		‘Morris the Mohel’ ‘Houndsditch Day By Day’ Sporting Times 11 Jan. 3: I vould’nt let my vife vipe ’er ponum on the same towel with ’er!
1894		Truth (Sydney) 14 Oct. 6/3: In the fifth round Griffo played havoc with Mac’s ‘ponum’ [and] Mac was bleeding like the proverbial pig.
1900		Sydney Sportsman (Surry Hills, NSW) 10 Oct. 1/2: Sorting me out, on account of the shape of my ponum, he blood thirstily informed me : he'd stand none of my shent-per-shent points worked into the advertising department.
1904		Sun. Times (Perth) 14 Aug. 4/7: George Rignold Bloom and his wife were there, his ponum took the bun.