Its true that fiat money's value is somewhat speculative, but speculation still has a specific meaning. It means you are investing not because you believe in the future value proposition of the asset (such as dividend payments, or liquidity value increase if all fixed assets of an enterprise were sold), but only because you expect the market price to increase. Often you expect the market price to increase for no reason other than you know many other people are speculating, so there is really no there, there.
