As the OP suggests, what exactly was "Communism" referring to in the early to mid-19th century?
My default presumption was that it was referring to the sort of communes you'd associate with Robert Owens, these sort of idealized planned communities where all property is common and people live cooperatively and so forth.
But reading up on the French Revolution, it occurred to me that it might actually have been meant to refer to the Commune, as in the Paris Commune of 1792-1794 and the particular social forces it represented. From that perspective, "Communism" to someone in the 1840s would mean identifying with things like the Commune, which would be seen as a vehicle for more direct control and action by the working class man on the street, versus more bourgeoisie institutions represented by things like the National Assembly.
Is that right, or am I off base?
Here's what the Oxford English dictionary has to say about pre Marx usage of Communism:
French communiste was used earlier (1769) with reference to participants in the collective possession of land (mortmain). The French term was also used for other kinds of collective ownership in the late 18th cent., e.g. with reference to the right of pasturing animals on common land (1789). It was also used from at least the 1830s to refer to adherents of François-Noël Babeuf (1760–97), militant French revolutionary. Coinage of the term in the sense ‘advocate or adherent of the theory of communism’ has been variously attributed to Pierre-Joseph Proudhon (1809–65), French editor, politician, and social theorist ( P.-J. Proudhon Qu'est-ce que la propriété? (1840) 326) and Étienne Cabet (1788–1856), French philosopher ( É. Cabet Comment je suis communiste (1840)). Both seem to have arrived at the term independently in 1840. For a full discussion of the origins and development of French communiste (and related terms) see Geschichtliche Grundbegriffe III. at Kommunismus.
And in the Communist entry there's this:
German Kommunismus is attested earlier (1794) in an isolated and apparently unrelated attestation with reference to the theories of Franz von Hebenstreit (1747–95), one of the Viennese Jacobins.
Sources:
"communist, n. and adj.". OED Online. June 2018. Oxford University Press. http://www.oed.com/view/Entry/37326
"communism, n.". OED Online. June 2018. Oxford University Press. http://www.oed.com/view/Entry/37325