The term "fascism" was used - to my knowledge, and limitedly to Italy, hence, properly, as "fascismo" - first, sparsely and in a merely descriptive sense, to refer to certain "liberal" groups of supposed republican-Jacobin origin within the works of reactionary polemists during the early XIX Century (for a few examples, see Francesco IV's La Voce della Verità and similar publications). In this context, the term would only be understood in its proper meaning thanks to its literal context: the use of the "fasces" as a Jacobin symbol had made it so that various political groups of republican inspiration had adopted it as a more or less informal denomination - the word fascio being already established to define "a bundle of sticks of things collected and fastened together such that a man can carry", and therefore, with its implication of strength out of unity of equals, being an ideal symbol for a political formation. Hence "their fascismo" would be understood as "their practice of forming these organizations".

The term saw a relative resurgence in the late XIX Century, due to the rise of the movement of the Fasci Siciliani - a large period of social mobilization and unrest of, very vague, socialist and democratic inspiration taking place in Sicily, but soon becoming a major source of concern for the national government which adopted strict repressive measures, targeting socialist, anarchist and other subversive groups. In this particular time period, a reference to fascismo would have been understood to describe that ongoing phenomenon. The Italian government had, anyways, interpreted it as an expression of rising socialist subversivism (or taken advantage of the circumstances to mount an anti-socialist campaign), which means that the Fasci Siciliani were almost never regarded as an autonomous ideological or social expression.

Their end and the subsequent period of instability during the "crisis of the end of the Century" led to the opening of a period of liberalization under the new King Vittorio Emanuele III and prime minister Giovanni Giolitti, when the word fascio continued to be used to refer to political organizations and groups of citizens; specifically to local organizations and not to "proper" political parties.

During the build up to the Great War, the use of fascio appears to become more distinctive, in so far as it represented an alternative to both "league" and "union" (terms apparently hegemonized by socialist and catholic organization) and remained distinct from parliamentary formations. This is probably among the reasons which led to its adoption by interventionist formations - mostly of so called "left-interventionism" - which shared a similar background (republicanism, irredentism, pro-French and anti-German sentiment) in opposition to nationalist and conservative interventionism (which originally supported for the most part an intervention on the side of the Triple Entente). During the war, the term fascio became widespread to describe interventionist and pro-war social-mobilization groups, of a somewhat trans-political character, until it was adopted, after the collapse of the Italian front at Caporetto, to describe a major "national-interventionist" parliamentary formation - the Fascio Parlamentare di Difesa Nazionale - specifically in opposition to the "defeatist" forces of Giolitti's "Liberal Union" and of the Socialist Party.

By the end of the war, the term fascio was almost synonym with "interventionism"; albeit not yet strictly speaking with "national-interventionism" (the drift towards "national-interventionist" and nationalist positions gradually eroded the political influence of the original "left-interventionist" formations), as there were various short lived "liberal-democratic" incarnations (such as a significant number of "Wilson's fasci").

That was the meaning of the word when Mussolini took part to the foundation of the first Fascio di Combattimento in Milan, on March 23^rd 1919 - one of the various intitiatives he promoted during his attempts to form a sort of coalition of the "interventionist" forces in preparation for the national elections of November 1919 (a project he often referred to as Intesa e Azione). The fasci, specifically targeted at "combatants", had to represent a part of this re-imagining of "interventionism" in the post-war scenario.

It's some weeks after their inauguration that Mussolini himself first adopts the word fascismo - still in a descriptive sense - to refer to this "movement of the fasci di combattimento". Their extremely modest numbers, and the complete failure of Mussolini's electoral project (with the apparent dissolution of whatever little forces the fasci had managed to collect in the meantime) meant that the term fascismo remained marginal at best; mostly used by the members of the fasci themselves to describe and promote their intitiatives.

It's only with the resurgence of the fasci - largely as instruments of the agrarian reaction in 1920-21 - and with the growing scale of "fascist" violence that the term "fascismo" begins to be adopted nationwide and by larger strata of the population to refer unambiguously to a social and political movement identified with the national leadership of Benito Mussolini.

And it's with Mussolini's appointment as Prime Minister in October 1922 that the international public opinion and political observers begin to take notice of the new phenomenon, and to seek to understand and interpret this "fascism" thing. Hence the first publications, either by foreign commenters or translated into English and French, which discuss the origin and character of Mussolini's "fascism". This is also the time when the term begins to be adopted internationally, either by groups imitating or anyways adopting Mussolini's "fascism" as a positive example, or as a disparaging term for groups of the authoritarian "national-right" (both these uses would increase and consolidate, significantly to my knowledge, during the mid to late-1930s when the Italian Regime's reputation became more unambiguously negative and within the context of the political polarization prompted by the Spanish Civil War).