I have coined a word. How do I get credit for it?
Unfortunately there is no agency (including Merriam-Webster) that we know of that keeps a public record of coinages of words, and more often than not, by the time a word has demonstrated enough frequent and consistent usage to merit entry into the dictionary, the source of its coining is too far distanced or obscure to confirm.
If you feel that you have developed or know of a word that could serve to better the English language, we can only suggest that you use the word as much as possible in your everyday discourse and see if it catches on with other English speakers and, more importantly, writers. For the purposes of ensuring credit for coining the word, you might want to keep on hand conclusive evidence that you are the originator of the word specifically, something that notes the word and the date (or at least the approximate date) that you created it. Should the word take hold and acquire enough popularity to be entered into a dictionary, you will then have concrete proof that you hold the earliest citation for it. You may even want to write or type the word on a postcard and mail it to yourself, as skeptics might be less likely to challenge the authenticity of an official postmark.
Be warned, though, that very few coiners of words throughout history have gained any notice as wordsmiths, and even fewer any renown. Perhaps, however, with the right approach you can counter that trend.