In a word, no.
First of all, there’s the thorny issue of defining what a word even is. Is a phrasal verb one word, or two? Is a proper noun a word? How about a persons’s name, like BreAzia? Or the names of Pokemon creatures, like Meowth and Psyduck? (I know plenty of 9-year-olds who will insist those are words!) Or proper nouns from famous fiction, like Slytherin, Alderaan, Klingon, and Scrooge? What if I make up my own word, like ponyfraggis? If that’s not a “word,” what is it? What about acronyms and abbreviations? (S.C.U.B.A. diving, anyone?) Or prefixes and suffixes? What about slang, jargon, loanwords, eggcorns, and Spoonerisms? Is zoot a word? (Most dictionaries will list zoot suit, but not zoot.) Is hors a word? What if I'm serving hors d’oeuvres?
Secondly, finding a word in several dictionaries can pretty much demonstratively show that something is a “word”, but not finding a word in a dictionary proves nothing. Language evolves; new words are added to dictionaries regularly (D’oh! I'll bet you already knew that), but words aren’t usually added until they’ve demonstrated sufficient durability. That means dictionaries are often five or ten years behind the corner bars, water coolers, sports arenas, and television scripts – but for good reason: dictionary editors don't want to add words into their dictionaries only to take them out again five years later.
Thirdly, there's plenty of scientific jargon that hasn't wormed its way onto dictionary pages yet. Even the phat OED doesn't list qubit yet (my spellchecker doesn’t like it, either), but our Peter Shor would tell you that it is a word faster than you can factor 15. Moreover, what’s true in science is also true in marketing; if 7-Up is the Uncola, does that make Uncola a word?
I don’t mean to sound Pecksniffian, but my answer to your question is a resounding, “No, of course not!” Rules, beyond dispute? Trying to pinpoint when a “real word” begins is like trying to figure out when life begins, or when the universe began.
If you believe in real words that aren’t in the dictionary (like Tinkerbell, for example), clap your hands.