fifth wheel

An unneeded extra, a superfluous person or thing. This expression was already listed as a proverb in the sixteenth century in a French collection; in its complete form it pointed out that the fifth wheel on a wagon does nothing but impede it (C. B. Bouelles, Proverbia Vulgaria, 1531). Thomas Dekker repeated it in a play (Match Me in London, 1631, Act I), again in fairly literal fashion: “Thou tyest but wings to a swift gray hounds heele, and addest to a running charriot a fift Wheele.” But it also was being used figuratively during this period, and has continued to be ever since.