British & Australian something that you say to a child in order to make them say 'please' or 'thank you'.
'Can I have a chocolate, mummy?' 'What's the magic word?' 'Please.'
What's the magic word?
A question posed to someone (typically a child) when they have asked for something without saying "please." A: "Can I have some money to go to the movies?" B: "What's the magic word?"