If something is said and people understand it, sounds like a word to me. If people didn't understand it, I would think they would rather say, "what do you mean?", than making it a word after a definition is explained. Or are there exceptions I'm not thinking of?
Dictionary or not, if people understand something, even if just locally, it's a word.
Of course, there is some irony in people seemingly claiming to have a mastery of language who do not know what the word 'word' means.
One example may be this David Cross bit I've heard, where he said 'irregardless' isn't a word, even though it's been used for a long time and is understood. However, it is considered nonstandard in at least some dictionaries.
There may be cases where something incorrectly thinks that a valid word isn't part of standard English even though it actually is. I would still include this in the scope of the question, because they they think it's wrong, whether they are right or not.
If someone is making a mistake, if it's still understood, it'd still be a word, for that moment, at least.
A more common example may be the use of "ain't".
(Kids exclaiming 'that's not a word' out of disbelief would be an exception, but I think it's a rather different usage.)