Green’s Dictionary of Slang

(S.Afr.) a friend, a chum, a pal.

1900		B. Mitford Aletta 66: By the time they are found the English will not be here to hang anybody and we, ou’maat – we shall have deserved the thanks of all true patriots. [Ibid.] 153: ‘I was not thinking otherwise, ou’ maat’ said Stephanus heartily.
1977		C. Hope Ducktails in Gray Theatre Two (1981) 52: Ou maat, jus’ pass me the keys for your jammie.
1985		B. Simon ‘Outers’ Born in the RSA (1997) 64: Be nice to each other my maatjies.