Green’s Dictionary of Slang

a mother.

1913		Sport (Adelaide) 3 May 12/2: They Say [...] That What’s up, Joe, don’t see you so often in Todd street. Does mater and pater object.
1918		A. Brazil Patriotic Schoolgirl 120: ‘I’ll call on Saturday afternoon at Brackenfield for you [...] The Mater will square your Head’.
1930		N. Lindsay Redheap (1965) 72: ‘He’s got no more right than a perfect stranger. Yet the mater encourages him’ .
1937		Duckett & Staple ‘Double Feature’ in N.Y. Age 28 Aug. 7/2: If you’ll pardon [...] the slang, mater...I’ll plant cha now and dig ya later.
1957		(con. WWII) ‘Weldon Hill’ Onionhead (1958) 30: Back with pater and mater the fifty servants.