What is the definition of a word or phrase that does not describe properly what it is or does? For example a black box flight recorder is not black but orange. Are there any other examples of such words or phrases?
It's called a misnomer - the name doesn't match the named.
Misnomer noun A wrong or inaccurate name or designation: ‘King crab’ is a misnomer—these creatures are not crustaceans at all - ODO
Here are some examples from wikipedia:
- Catgut is made from sheep intestines.
- French horns originated in Germany, not France.
- The "funny bone" is not a bone—the phrase refers to the ulnar nerve.
A seemingly absurd or contradictory statement or proposition which when investigated may prove to be well founded or true:
the uncertainty principle leads to all sorts of paradoxes, like the particles being in two places at once
A combination of statements, ideas, or features which are opposed to one another:
the proposed new system suffers from a set of internal contradictions
While a modern-day black box is painted bright orange to help investigators find them, early versions were painted black, and the name stuck.
I suggest that this is an idiom:
Idioms are a group of words established by usage as having a meaning not deducible from those of the individual words. Example of idioms are "rain cats and dogs" and "see the light."
There are several lists of idioms on the Internet, including:
It's all there in the tag definition on this very website!
I can think of three examples immediately;
which nothing to do with elbows or grease, but means hard physical work
which is an inflammation of the elbow area, but not always caused by tennis.
which is an adjustable wrench, unfortunately has very little to do with monkeys.
which isn't a dog, it's a sausage.
For a definition, I think I'd go with;
colloquialism - a word or phrase that is not formal or literary and is used in ordinary or familiar conversation