“on hiatus” VS “on a hiatus”

Question

In dictionaries (example 1, example 2) it says that “hiatus” is a countable noun which is usually singular, but I see it being used as an uncountable noun as well in phrases like

• Two of my colleagues went on hiatus.

• I ate too much when I was on hiatus.

My question is, is “hiatus” actually a variable noun which can be used as an uncountable noun in the set phrases “be on hiatus” and “go on hiatus”? If so, doesn’t it mean the dictionaries are wrong? I see it being used as a countable noun as well in those phrases though. So I think instead of the sentences I gave above we can say these as well, right:

• Two of my colleagues went on a hiatus.

• I ate too much when I was on a hiatus.

Note: The context for the first sentence is, my colleagues took leave from work so they don’t go to work at the moment. In the second sentence, I say that I ate too much when on leave from work.

Answer 1

"Hiatus" is a countable noun because it can be used countably. But in the sentence "Two of my colleagues went on hiatus" it's used in an uncountable way, both grammatically and semantically. The phrase "on hiatus" functions more like an adjective describing the state of the workmates, rather than a preposition connecting the workmates to the noun "hiatus".

It's possible, however, that this uncountable usage of "hiatus" is idiomatic to the phrase, "on hiatus". This would mean the dictionaries aren't wrong. I can't think of any other ways "hiatus" is commonly used in a clearly uncountable way. For a word to be considered uncountable, it has to be used that way in lots of different contexts, not just in one phrase.