One reason I collect dictionaries and writing reference books is to add to my knowledge. One thing I have learned, even with those large, unabridged dictionaries, not all words make it into the dictionary. Why? It may be the word is too specialised and has fallen into disuse. And, I have just such a word for you today, deucer.
According to the Dictionary of Word and Phrase Origins, deuce comes from both the Latin (duo) and French (deux), both meaning "two." But the word "deucer" has a number of meanings, the most common is that it can be used as another word for a two-dollar bill. In underworld slang, it is a person serving a two-year sentence in jail. Baseball jargon uses it to mean either a two-base hit or the second game of a double-header. In racing circles, it is the horse that finishes second. In circus and vaudeville, it is slang for the second spot on the bill.
So, though you may be hard pressed to find deucer in a dictionary, it is a word that can and should be used in your writing. And, with the wide array of uses listed above, I'm sure you can find some way to sneak it into a project.