Green’s Dictionary of Slang

(Aus.) the vagina; thus by metonymy, sexual intercourse.

1950		‘No. 35’ Argot in G. Simes DAUS (1993).
1967		‘Whisper All Aussie Dict.’ in Kings Cross Whisper (Sydney) xl 4/4: smooy: ‘A bit of smooy’ to make love. Sometimes crumpet, used by the British.
1968		J. Beede They Hosed Them Out 191: A hostel for land army girls on the other side of the drome. This, he declared, offered more smooey than you could poke a stick at.
1977		J. Ramsay Cop it Sweet 83: smooey, bit of, fornication [DAUS].