3 Answers

" To buy something that proves be worthless."

A lemon is a defective car that is found to have numerous or severe defects not readily apparent before its purchase. Any vehicle with these issues can be termed a 'lemon,' and, by extension, any product which has major flaws that render it unfit for its purpose can be described as a 'lemon' (WIKIPEDIA)

In 1910, the rotating slot machine appeared as a device for dispensing chewing gum and gave us the symbols still used on slot machines today.  The spinning flavors were cherry, orange, and plum.  Each wheel had a bar reading "1910 Fruit Gum," and three of those in a row paid off in a jackpot of gum.  But, also like today, if any row turned up a lemon there was no payout at all, which gave us the disappointed expression, "It's a lemon."