I have about 30 old tool books including the "Dictionary of American Hand Tools" that contains illustrations of every hand tool type made for the last 150 years and a brief description. The only tools remotely resembling this unknown are a carriage (or coach) makers spokeshave (due to the long 18" length) and a riding boot leather shank burnisher. Both are long and both have double wood handles. If it is a spokeshave, the center parts that would show wear are missing and what is left would show virtually no wear to the metal parts. If it is a shank burnisher, the metal parts should exhibit smoothness from burnishing leather over a period of time. If there is no wear showing, I do not think this is a burnisher. If it is neither one of these, I am at a total loss.