[Wobbles42]

The difference between phrases and "words with spaces" is addressed.

The confusion might be that this seems to be a spectrum rather than a binary phenomon.

We have single words at one extreme, ordinary sentences at the other, and in the middle we have idiomatic assemblies of words that span a range of substitutability.

"Hot dog" and "Saturday night" are arguably great examples, because they exist at the opposite extremes of the spectrum. Saturday night can retain some of the original meaning following substitution, whereas hot dog almost deserves a hyphen.

[quesera]

I disagree that "saturday night" ever means anything other than the literal meaning of the nighttime of the day of saturday.

You can argue that there's a connotative association with the phrase. Sure. Just like "beach weather", or "blizzard conditions". But that doesn't make "saturday night" special in any way.

[Wobbles42]

I am with you on the literal definition there.

I wonder if the connotative association is exactly what we are trying to capture here though, and if those other phrases also fit in at the "separate words but slightly special" end of the spectrum.

There is meaning being communicated in all of those phrases that would be obvious to most or all people who are embedded in the language and culture where they are used, and which transcends the definitions of the individual words themselves.

It seems that there are several axis here -- how explicit is meaning, how atomic, how literal, how substitutable are the individual words -- and all vary continuously.

That might all seem needlessly pedantic for the question of "should it warrant a dictionary entry", but if you are trying to extract all information encoded in a verbal exchange, they might be useful concepts.