Difference between pigovian tax and sin tax? Could they be interchangeably used? Or, is one subset of the other?
A pigouvian tax is on goods or services that are known to have negative externalities, and for which some estimation of the economic value of those negative externalities can be made, and is there to correct the market failure. Its goal is to improve economic efficiency.

A sin tax is on goods or services judged to be morally negative. Its goal is to reduce consumption and/or appease the moralists and/or raise revenue in a way that is less likely to be successfully opposed.