Which world is a plutocracy?
We're that one in practice.
Also, language evolves rapidly, terms change meanings over time often.
Try getting 100 random people or even college graduates and try to get agreement on the modern meaning and usage of socialism.
Words and terms evolve, even dictionaries make regular changes to react to already in use changes over time.
I think the more modern usage is 1st world= developed socioeconomic infrastructure 2nd world = developing nation 3rd world = impoverished/underdeveloped nation.