Definition: something extremely expensive
Example: Randolph wanted an indoor swimming pool. As much as Julie wanted one herself, she had to be the reasonable one. “Are you kidding? That would cost an arm and a leg!”
Okay. Let’s get the most commonly believed origin story out of the way, because there’s no truth to it.
Portrait painters, over the past centuries, had a fixed price for a standard head and shoulders portrait. If you wanted the torso included, the portrait would be more expensive. If you wanted the full body painted, that would be still more. Though it is likely true that a full body portrait would cost more than a traditional head and shoulders one, it is unlikely the artists charged by the limb! On top of that, the phrase doesn’t appear to have entered the language until after the Second World War, well after the age of portrait painting.
It is more likely to have come from an earlier nineteenth century phrase, often expressed in terms similar to ‘I’d give my right arm for that’, though there were left varieties of the phrase, as well as other limbs and organs quoted. In other languages, there are phrases that seem to support this. In France, something may ‘Cost the eyes from your head’. In Bulgaria, something may ‘Cost your Mother and Father’.
Another explanation ties in with the idiom’s introduction to the English language after the war. Many soldiers returned home to America (where the phrase appears to have originated) missing limbs. This indeed was a high price to pay for their country. It had cost them an arm and a leg.
I really don’t want to know where Iddy got his extra limbs from.