Sentence:  Such an expression is <WSD>mad money</WSD>, noted as early as 1922 by Howard J. Savage ("Dialect Notes" 5:148) at the end of an article on Bryn Mawr slang. Savage's definition is 'money a girl carries in case she has a row with her escort and wishes to go home alone.' 
Meaning of the word marked with <WSD> tags:  A sum of money kept in reserve or to insulate oneself financially in the event of the sudden breakdown of a relationship in which one is economically dependent.