Australian and New Zealand slang meaning to cheek, sass, or make cheeky remarks to someone in a friendly but impertinent way.
Possibly from imitation of the sound of cheeky talk, or from British 'cheek' with an altered pronunciation and the -ack ending for emphasis.
Chiack is purely Australian/New Zealand English—it captures a very specific cultural attitude of friendly mockery that wouldn't translate the same way with 'sass' or 'cheek' in other Englishes.
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