Definition of pin money noun from the Oxford Advanced Learner's Dictionary

 

pin money

 noun
noun
BrE
 
; NAmE
 
[uncountable]
 
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a small amount of money that you earn, especially when this is used to buy things that you want rather than things that you need She earns a little pin money doing ironing for other people. Word Origin late 17th cent.: from pin in the sense ‘decorative clasp for the hair or a garment’ + money. The term originally denoted an allowance made to a woman for dress and other personal expenses by her husband.
See the Oxford Advanced American Dictionary entry: pin money