Rationalism in philosphy means more than being rational: it is the belief that you can deduce true knowledge about the world by mere thinking ("apriori synthetic" knowledge).
Imagine you are Einstein, and you have derived relativity from a few axiom, if you are still interested in experimental verification of your theory then you are an empiricist. If you say: I know for sure I'm right no need for experiments at all - you are a rationalist.
Modern science is mostly empiricist, maybe hardcore austrian economists are rationalists (for them economy is derived from praxeology, experimental verification is not possible and not needed)
Imagine you are Einstein, and you have derived relativity from a few axiom, if you are still interested in experimental verification of your theory then you are an empiricist. If you say: I know for sure I'm right no need for experiments at all - you are a rationalist.
Modern science is mostly empiricist, maybe hardcore austrian economists are rationalists (for them economy is derived from praxeology, experimental verification is not possible and not needed)