Does this expression mean a fifth wheel as in an odd person out, or a fifth wheel as the connector between a tractor-trailer? Or both?
As in an odd person out, yes. It equates to the English "Third wheel" (Or fifth wheel if that happens to work in your dialect)
That also works in French, where you'd be "la cinquième roue du carrosse" (the fifth wheel of the carriage). At least you get to be part of a luxury vehicle from fairy tales. :)
In Lithuanian we say something that would translate to "The fifth leg of a dog" :)
Never heard of that expression before and I'm from Lithuania as well. Great to learn new things! :)
I will have to remember that one Kristina.
In Polish we have the same expression, "Piąte koło u wozu".
In Italian: "l'ultima ruota del carro" which means "the last wheel of the carriage". The last wheel is the spare wheel which happens to be the fifth.
I think "Third wheel" is best in English. Fifth wheel makes it sound more like a spare wheel for you car...
Fifth wheel can also refer to a single person going along with two couples, but I do agree that third wheel is more common situation and expression.
This can technically go as high as you want. I once referred to myself as the 17th wheel or something, because I was eating at a restaurant by myself and the rest of the tables were couples (and I counted them).
Third wheel of a bike or fifth wheel of a car. ☺
Although I do think that functioning tricycles are more common...
Should one always use the definite ending on a noun when one is describing it as first, third, fifth and so forth?
Preferrably, but not necessarily. You could say it in the indefinite, but then add the article too: Vi behöver ett femte hjul ("We need a fifth wheel").
Much like the German term for 'third wheel', das funfte rad am wagen.
Except that das fünfte means the fifth ;)
We have an exparassion in Hebrew: "גלגל חמישי" (galgal khamishi) which is translated to, and means, excactly the same (:
Just like me