Green’s Dictionary of Slang

(Aus.) in poker, a flush.

1984		J. Meredith Learn to Talk Old Jack Lang 19: barmaid’s blush: a flush.
2002		Pete’s Aussie Sl. Home Page 🌐 barmaid’s blush: a flush, as in poker.
2009		S. Butler Dinkum Dict. 10: barmaid’s blush: a flush, as in poker.