[aaronblohowiak]

I think spend-thrift means tight with your money, or parsimonious if you prefer.

[amvp]

To be thrifty, is to be careful with your money. Oddly though, a spendthrift is the opposite. http://www.thefreedictionary.com/spendthrift

[gjm11]

Here's how the etymology works:

thrive: prosper

thrift (~= having-thrived): prosperity, hence money

thrifty: acting so as to get or maintain thrift, hence not spending much

thrift (derived meaning): the quality that thrifty people have; again, not spending much

spendthrift: a person who spends his or her thrift; hence, someone who spends a lot

spendthrift (derived meaning): the quality that spendthrifts have; that is, spending a lot.