What, exactly, does the prefix quasi mean, and can it stand on its own? The term, from Latin, is used as a qualifier to denote that something resembles or is like something but is not exactly equivalent, and, yes, quasi is an adverb.
Quasi often appears in phrasal adjectives as a more formal alternative to “kind of” or “sort of”: A quasinomadic culture, for example, is one that has some but not all characteristics of a purely nomadic society. Something quasihistorical is based on fact but partly or mostly fictitious, such as the tales associated with King Arthur. A quasimilitary organization is one that resembles a military organization but does not function under the authority of a formal government, such as a rebel militia, or does not have a military function, such as the Salvation Army. (Words beginning with quasi are often seen hyphenated, but the hyphen is unnecessary.)
Quasi may also, on its own, modify a noun, as in “quasi leader” (such constructions are often unnecessarily hyphenated), or even, rarely, a verb.
The name of Quasimodo, the titular protagonist of The Hunchback of Notre Dame, is related. Because, as an infant, the character was abandoned at Notre Dame on Low Sunday, the first Sunday after Easter, he was named after the first words uttered during the Catholic Mass held on that day: “Quasi modo geniti infants” (“as newborn babes”). (I had always assumed the name means “half formed.”)
Two words, one common and the other obscure, are based on quasi: Quasar is a contraction of “quasistellar radio source” (Merriam-Webster hyphenates quasistellar, but for consistency, I’m closing it), and quango is an acronym for “quasi-non-governmental organization”; it’s also employed as a prefix in quangocracy and quangocrat.
Quasi is also seen as the first element in the odd British English term quasihemidemisemiquaver (styled semihemidemisemiquaver in American English), which refers to the extremely short 128th note in music. The shortest named note is the demisemihemidemisemiquaver, or 256th note; hemidemisemiquaver is the name of a 64th note, and demisemiquaver and semiquaver, respectively, denote the two next-shortest notes in British English. (In American English, they are referred to simply as 32nd and 16th notes.)
The prefixes semi-, demi-, and hemi- (the first two from Latin, and the last from Greek), meanwhile, all mean “half” (the first two can also mean “partly”). Semi is perhaps best known to readers of American English as the abbreviated term for a large tractor truck that hauls freight; the full term is semitrailer, which refers to the trailer with no forward wheels that is attached to such a truck. Demi appears in words such as demigod, the label for a lesser god, and demimonde (French, literally “half-world”), which denotes the culture outside of polite society. Hemi, among other usages, precedes sphere to refer to one-half of a planet or other globe-shaped object.