More Idioms

What is an idiom, anyway? Obviously any common use of language is idiomatic (as opposed to being non-idiomatic). A phrase like "common use" is idiomatic because it sounds natural, but it is not an idiom.

An idiom might be defined by being

(1) More than one word?

(2) Unpredictable in meaning from the primary dictionary definitions of the component words?

(3) Metaphorical or figurative in some way?

I put question marks here because I am not sure. For example, the idiom "begging the question" is not metaphorical. Nor is "echar de menos..." (missing something). Echar mean toss or throw, but missing someone does not involve throwing in the metaphorical sense. Buying the farm is a metaphor, but not all idioms are of this type.

Can an idiom be only one word? Idiomatic uses of words as exclamations or greetings might fall into that category. "¡hombre!" in Spanish can mean "of course what you're saying is true, but.... " or "what the hell" any number of other things. Calling someone "m'hijo" when they are not your son is idiomatic too, right? Or using the word "cielo" as a term of endearment.

Are one word idioms different than fixed phrases? Or are they fixed phrases that just happen to have one word in them? Like "Vaya..." meaning "would you look at that, it's pretty ridiculous."

So what we've discovered so far is that idioms are phrases whose meaning is not determined by the primary lexical definitions of the component words, which may or may not be metaphorical, which are can be words or phrases. Idiomatic words tend to be terms of endearment, exclamations, greetings, or possibly one-word metaphors. They have to be familiar parts of the language. I can say I'm under the weather but not "I'm off my garlic." That would be a perfectly acceptable idiom, but it's not because I just invented it on the spot.