I agree that they're not party alignments, but do they really have concrete meanings? In my experience they seems to mean different things to each person who uses them.
> Capitalism is an economic system based on the private ownership of the means of production and their operation for profit.
Both of those definitions encompass a wide range of economic systems, but they are fixed definitions. There's never going to be some inversion where "socialism" suddenly describes the private accumulation of capital.
Is a market-based system with strong progressive taxation and a large basic income capitalist? Is it socialist?
IMO it's not obvious and you could argue it either way for both terms.