5th

Someone who has no real place or purpose in a situation, likened to a superfluous extra wheel on a four-wheeled vehicle. I didn't realize that the party was for couples only, so when I showed up alone, I felt like a fifth wheel.

A phrase associated with Guy Fawkes Day, November 5. Guy Fawkes was a conspirator in the thwarted Gunpowder Plot, which would have killed King James I and blown up Parliament on November 5, 1605. Primarily heard in UK. A: "What exactly is Guy Fawkes Day anyway?" B: "Ah, remember, remember, the fifth of November."

Fig. an unwelcome or extra person. I don't like living with my son and daughter-in-law. I feel like a fifth wheel. Bill always begs to come on camping trips with us, but really, he's a fifth wheel.

An extra and unnecessary person or thing, as in He was the only one without a date, so he felt like a fifth wheel. This expression, which alludes to an unneeded wheel on a four-wheel vehicle, may have originated as long ago as 1631, when Thomas Dekker wrote Match Me in London: "Thou tiest but wings to a swift gray Hounds heel, And addest to a running Chariot a 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.