⇨ zack; zacnoun a sixpence; the sum of six pence. Origin unknown. Perhaps from Scottish dialect saxpence (sixpence), or possibly Yiddish from German sechs (six). After the introduction of decimal currency in 1966, it came to mean 'a five-cent piece', or its value, a similar coin with about the same comparative value; dying out from the 1980s, now seldom heard AUSTRALIA, 1898.► not have a zackto be broke AUSTRALIA, 1989.► not worth a zackworthless AUSTRALIA, 1962