The definitions have changed over time. Republicans are liberal in the sense that most of them believe in personal liberty and freedom of speech.
Republicans tend to be fiscally and socially conservative however. Which is why they are referred to as conservatives.
The word liberal, when used
pejoratively, means someone that wants the government to fix everything, control everything, and limit what people can say or do. When someone in the US uses that term, that is what they mean.