Garner, Dict. of Modern Amer. Usage, p. 547:
quasi ... means "as if; seeming or seemingly; in the nature of; nearly." In legal writing, 'quasi' may stand alone as a word, but as a prefix it's generally hyphenated. The term has been prefixed to any number of adjectives and nouns, e.g., 'quasi-compulsory,' 'quasi-domicile,' 'quasi-judicial,' and 'quasi-monopoly.'
Chicago Manual of Style, 15th ed., p. 306:
7.90
quasi: a quasi corporation, a quasi-public corporation. (Open before a noun, hyphenated before an adjective.)
__________
Several online style guides agree with Chicago that it should be hyphenated before an adjective but not before a noun: <
http://www.google.com/search?hl=en&q=quasi+hy...>. This may explain the dictionary listings for it as a separate word, in which all the unhyphenated examples do indeed seem to be before nouns.
Like all the other native speakers so far, I don't think it should be used as an adverb standing alone, that is, not immediately followed by a noun or adjective. I would revise Marc's example sentence as follows:
· thus a quasi-infinite sequence of ...
And in Norbert's and Pachulke's examples I would substitute 'almost' or 'practically':
· almost as a nation of her own
· practically instantly / almost immediately