Definition of "unbirthday" [unbirthday]

• A day that is not one's birthday but is celebrated as though it were. (noun)

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• "Des has his "unbirthday" party at school today, and I remembered how scrumptious those cupcakes of yours are, so looked up the recipe and made them."
• "Tragically, she died of cancer when I was 10, but she did her bit – buying me "unbirthday" presents throughout the year, and taking an interest in everything from Brownie camp to my favourite dolls."
• "I recommend a funny hat, a tea party and the unbirthday song."