- The definition of spendthrift is wasteful or extravagant.
An example of spendthrift used as an adjective is a spendthrift teenager.
- Spendthrift is defined as a person who overspends, or who spends money in an irresponsible way.
An example of a spendthrift is a person who spends hundreds of dollars on purses and shoes she can't afford.
Origin of spendthriftspend + thrift, accumulated wealth (obsolete).