@cicerone imposter,
Merriam:
a theory advocating elimination of private property
a system in which goods are owned in common and are available to all as needed
a doctrine based on revolutionary Marxian socialism and Marxism-Leninism that was the official ideology of the Union of Soviet Socialist Republics
a totalitarian system of government in which a single authoritarian party controls state-owned means of production
A final stage of society in Marxist theory in which the state has withered away and economic goods are distributed equitably
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So, there are varied definitions due to how this system was put in practice. The definition about a single totalitarian gov't owns production is what communism came to be known as, as a result of the soviet union originally being called communist. But that is not in the original definition.
The original definition, per the revolution was that workers seized control of production and it was assumed that from there, things would defacto become equitable. Basically without top down management. When Lenin took over he said there would have to be a period of transition where the few would have to rule because the masses were too stupid at that point - which he called advanced socialism, but eventually folks would become educated and power would transfer to the people. This is the last definition that Merriam shows..
That never happened. Probably Lenin, certainly Stalin had no intention of giving up power. So, the SU remained an 'Advanced Socialist' state. (this is govt of the soviet union 101)
However, because their revolution was ostensibly communist, they were called communist and when other countries followed suit and had similar dictatorships, communism began to be associated with that style of governance..hence that dictionary definition.
These are important distinctions because there output, results and practices can be quantified, referenced, are on a scale. So, when you look at practices, they are closer to socialism than a more pure definition of communism. I personally don't think the definition of a totalitarian state controlling production to describe communism is helpful because, 1. that's not original definition and 2. related, its not the only type of communism that can be conceived. That definition is too limited. Which is probably why they included the other definitions in the dictionary you referenced..