off season adj (off-season when prenominal)
- denoting or occurring during a period of little activity in a trade or business
- such a period
- in an off-season period
But people also usually say "in winter", not "in the winter", like:From the WRF dictionary. I would say many people would omit the hyphen in your second example. Replace the "off season" with the word "winter" and see how you think it sounds "Although it was winter, ..."
Sorry, but I don't understand what you mean and what it has to do with an adjective.If you accept that it could be either with or without the article, maybe "the" is preferable here give a hint to the reader that what is coming is a noun modified by an adjective. "Off" doesn't look much like an adjective, and "in off" can be confusing.
I see both sentences in #1 as saying about a particular hotel and off season in generalThe second sentence is just stating a situation in general.
you may compare with the following sentence:
The water we drank last year had a lot of chlorine in it.
Water has a lot of chlorine in it.
Do I understand correctly that you mean that "in + the + adj + noun" is just an idiomatic collocation?I don't know how to understand "off season" as a noun except to see "off" as in definitions 1 or 4 for "off" as adjective in the WRF dictionary, and to see season as another noun that "off" modifies.
If that doesn't appeal to you, and you'd rather just consider "off season" as a noun without further analysis, "in" immediately followed by "off" is still a confusing collocation. I think that preceding "off season" with "the" prepares the listener or reader for a noun.
You asked why "the off season". That's what I'm trying to answer for you. "In the winter" is accepted usage. So is "in the off season". "In off season" may be, but it is hard to read.