1875, from Italian Mafia "Sicilian secret society of criminals" (the prevailing sense outside Sicily), earlier, "spirit of hostility to the law and its ministers." A member is a mafioso (1870), fem. mafiosa, plural mafiosi, and this may be the older word in this sense. Arabic is often cited as the ultimate source (the Arabs ruled Sicily for more than two centuries in the Middle Ages), but which Arabic word is a matter of disagreement.
The immediate source of mafioso, then, would be 19c. Sicilian mafiusu, "signifying a bully, arrogant but also fearless, enterprising, and proud" [Gambetta], who favors as the Arabic source an adjective from marfud "rejected."
According to this source, marfud ("rejected") became the Sicilian marpiuni ("swindler") and from there to mafiusu.
As often happens when I read etymologies of English words with Semitic roots, I wonder if there is a cognate in Hebrew. Well, this is one I would never have expected.
To find a Hebrew word related to marfud, we need to look a seemingly unrelated Hebrew root: פצר. It appears in the Bible seven times - six of which are in the kal form - patzar. In all of those cases it means "to implore, to beg earnestly." Modern Hebrew uses the hifil form of the verb, hiftzir, to mean "implore" as well. Klein writes that it is a secondary form of the root פרץ - "to push, to break through." That root can also mean "to spread, to extend."
This sense of "spreading, extension" is how classic commentators understood the use of פצר in its seventh use, in Shmuel I 15:23. The prophet Shmuel is castigating Shaul, the king, and says:
כִּי חַטַּאת־קֶסֶם מֶרִי וְאָוֶן וּתְרָפִים הַפְצַר
This is a notoriously difficult phrase to explain. It ends with the words utrafim haftzar (our root). Rashi says it means "an addition", and in that light, ArtScroll translates the phrase as:
"For rebelliousness is like the sin of sorcery, and verbosity [haftzar] is like the iniquity of idolatry"
However, modern translations, like the JPS have a different interpretation. They offer:
"For rebellion is like the sin of divination; defiance [haftzar], like the iniquity of teraphim"
Translating haftzar as "defiance" provides symmetry with the first half of the phrase, where everyone agrees that meri means "rebelliousness." And there is linguistic support for this translation as well.
David Yellin wrote in an essay, "Forgotten Meanings of Hebrew Roots in the Bible" (published here, and quoted by Stahl in his etymological dictionary of Arabic) that this use of the root פצר is unrelated to the other six, and based on cognates with other Semitic languages should be translated as "defiance." One of those cognates is the Arabic rafad - "to reject," which is the source of our word marfud above.
How did he get from fatzar to rafad? Through a number of phonetic shifts. First of all, the Hebrew tz sound can become d in Arabic (for example the Hebrew רמץ remetz becomes ramida in Arabic, the source of the month Ramadan.) And then through metathesis, fadar became rafad.
Quite a journey, no? So how can you remember that "mafia" and fatzar are cognate? Just think of a mafioso imploring someone to not be defiant...