"Nooooooooooooooooooooooooooooooooooooooooooooooooooo" is an expansion of the word no, a word which by itself indicates negation, but which is hereby really, really, really intensified by the introduction of fifty additional letters "o" (for a total of fifty-one, including the naturally occurring first "o"). This happens to be the largest number of added regular lowercase o's -- that is, naturally, an "o-string" -- which this noder was able to find (by an industrious search) to have actually been used in a real and genuine published book, as seen on Google. The book, by the way, is called "Apeland" and was authored by one Paul Allen all the way back in 1976.

The full context of use, as available in "snippet view" (here, if you doubt) is:
Margaret's soft fur pressed to T.; the father saw the passion of the embrace, the huge shoulders tensed and tight in ardor, the son's bent back as she pressed upon him "Nooooooooooooooooooooooooooooooooooooooooooooooooooo! (...")
Sadly, Google deigns to reveal no more of the text in that selection, and what little there is of it is like "Jesus Christ what-the-fuckall sense does that make?!?!" Just going by the title and that baffling bit of text, I'd guess there's some weird kind of monkey-manic bestiality at play there, hence the prompt for so goddamn many o's in the "no." I mean, seriously, what kind of sick, perversion of mind would it take to find pleasure in an account of a human mating with some ape-like creature? .... Oh. .... Well anyway.

In searching for the longest string of "no" o's, I went to Google's book search only after concluding that regular Google was flat useless. The liberal nature of the availability of pouring one's brain farts onto the Internet has made it possible for idiots (or, who knows, they may be geniuses) to post "no's" with o-strings which far exceed Google's capacity to actually hang onto a length of text as a search term.

There were, naturally, some itinerant hits for greater o-string lengths, but these were by and large misreadings from books of statistics which, for whatever reason, had a table with a value n for which that particular value yielded naught but naughts for the whole length of the table, as in:
y|00021|00045|00002|00000|00003|00002|00000|00023|00000|00000|....
z|00001|00017|00000|00000|00001|00000|00000|00004|00000|00000|....
n|00000|00000|00000|00000|00000|00000|00000|00000|00000|00000|....

And so forth for however many more rows. There was, by the way, one other plausible return on an expanded word "no," from "Satan's Dark Angles" by one Rick Magers, date uncertain:
Another voice roared across the sky as Satan lunged to grab the bolts of lightning. NOOOOOOOOOOOOOOooooooooooooooooooooooooooooooooooooooooo. Satan screamed as he grabbed one bolt—then another—and another.
Yep, that's fifty-five o's. But, will you look at that, fourteen are done up with garish capitalisation, symbolic of who-knows-what, perhaps a sticky caps lock key gone unnoticed in the fervor of pumping out the grand finale to a novel wherein Satan seeks to prevent God from destroying the Earth, after Satan has so successfully brought about war and corruption -- apparently to the surprise and consternation of the (therefore necessarily non-omniscient, perhaps really even non-Creator) top-dog deity showcased therein. Still, it's less fun to talk about then the Apeland hit, so there's my reasoning.

Beyond that, even Google is not helpful. Other than a few instances of mistaking lengthy statistical charts for useful negation, it tells me only:
Your search -
Nooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo ... - did not match any documents.

Suggestions:

Make sure all words are spelled correctly.
Try different keywords.
Try more general keywords.
For the record, that's sixty-nine o's before the ellipsis (though I'm elsewise told the hard limit is 128 characters). No speculation on how Google arrived at that cutoff. By comparison, there must be some irony in the fact that what is quite possibly the most famous o-string ever vocalised -- that of a newly minted Darth Vader in learning that he, in his anger has killed his own beloved Padme -- appears nowhere in the original script for Star Wars: Episode III - Revenge of the Sith. That writing finds reference only to Vader's 'scream of rage,' and not the lengthy tonal descending "no" injected into the part by James Earl Joooooooooooooooones.

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