I have two questions.
- Is there a noun for something which should be deferred?
- What would be the opposite for something which should be "fetched later"?
It's not exactly an everyday word, but deferrable - [item] capable of or suitable or eligible for being deferred is listed as a noun by Merriam-Webster.
The fact that it's not common isn't an issue - the meaning should be obvious on first encounter. Contexts vary, but often a deferable (my preferred spelling) means a "major purchase" (car, house, etc.) that can be delayed if money is tight - as opposed to non-deferables (food, toilet paper, etc.).
I would just refer to something that has been deferred as "the deferred".
"Defer" can be used on a wide range of things e.g. Decisions, tasks, chores, events, and so, the common practice would be to add "defer" before the thing:
I don't think there is a single word for either of these concepts. Possibly "restoree" might fit for something which had been deferred but has now been fetched, but that's not quite what you are asking for.
I would normally call something which should be deferred "something which should be deferred". Beyond that, I would have to start artificially constructing words like "deferand", which I don't think would help.
Here are my suggestions:
As a Noun, it means a subsidiary or auxiliary thing.
In the world of college admissions, a student who should be deferred would be waitlisted.
I know of no inverse of waitlisted.
The question seeks a noun for "something which should be deferred", or "something which should be fetched later", and also seeks a word having opposite meaning. I'll present pairs of words that are apposite and opposite, even if not always nouns. Also, as other answerers have done, I'll mostly ignore the should of the question, and instead offer terms for something that is deferred.
• masses ("lower classes") and elite ("choicest or most select of a group")
• sidetracked or sidelined and mainlined
• waiters and rushees, used figuratively
• NIP (not-important person [possibly a neologism]) and VIP (very-important person)
• backlog ("accumulation or buildup, especially of unfilled orders or unfinished work") and expedited ("accelerated; executed or dispatched quickly").
Summary: backlog may serve well for "something that is deferred", and elite for "something that is expedited". They are opposites of other terms mentioned; but not being apposite, are not opposites of each other.
Oppsite of something that should be "fetched later"...
"of immediate importance" / "of immediate import"
"of less importance" / "of less import"
"unexpeditable" (although this would mean Can't hasten rather than shouldn't.)
How about "Raincheck"? - not sure whether it fits in.
In answer to the title question, perhaps "continuance" or "contingency" would work. Although the first word has a specific definition in legal practice, it can easily be extended to other matters as well.
That said, when you can't find related words, find a synonym and start exploring those words. You will probably come up with something eventually.