I'm looking for a specific word (that is slipping my mind) that means "not allowed to be changed" or "has to be taken as law". The word I'm thinking of sounds something like "invaluable" or "inviable". An example of how to use it would be "Since the CEO likes it, this feature is ___ "
You can use the adjective immutable:
unchanging over time or unable to be changed.
Got it- the word is "inviolable"
Definition from Merriam Webster:
1: secure from violation or profanation
2: secure from assault or trespass
"Inviolable" at first glance doesn't precisely fit my example sentence: "Since the CEO likes it, this feature is ___ ". However, when emphasizing the importance of the feature in question- to the point of making it sacrosanct- the word works.
Stretching the definition of "single word" slightly, and it doesn't sound like the word you were thinking of, but perhaps (depending on the context) non-negotiable might do?
Since the CEO likes it, this feature is non-negotiable.
Which would work well if the context is something like:
We need to remove some features from this release due to time constraints. Can <this feature> be removed?
Sorry, since the CEO likes it, this feature is non-negotiable.
This isn't a single-word answer because it sounds more natural, especially in speech, to say that a thing is "set in stone" rather than using a single-word. It's also short enough that it doesn't disrupt the flow of the sentence. Also, Merriam-Webster has a few alternatives for this phrase.
So, my answer would be:
Since the CEO likes it, this feature is set in stone.
Cambridge definition (emphasis mine):
set in stone
to be very difficult or impossible to change:
The schedule isn’t set in stone, but we’d like to stick to it pretty closely
A very similar alternative, albeit strange sounding in spoken English, is enshrined. (Thanks to Peter for the suggestion.)
From Merriam-Webster (emphasis mine):
Examples of enshrine in a Sentence:
Some teachers tend to enshrine their personal preferences as sacred rules of English grammar.
By the time the monarchy was restored in 1660, the idea had taken hold that the spaces should be open to the public, a concept that was eventually enshrined in law in 1851.
Another alternative is must-have
Since the CEO likes it, this feature is a must-have.
so important that there cannot be any change or question
Based on your description, I think this fits your criteria.
Unalterable sounds closer to what you mean, at least to me. Immutable while considered a synonym to unalterable has a more permanent ring to it, meaning even if change was required, it is impossible to happen.
According to the example in this link , there seems to be a condition for change when unalterable is being used as word.
the constitution was unalterable without the king's consent
So your "not allowed to be changed" aspect of the question means it could be changed if needed, and unalterable seems like the best option.
I think something along the lines of mandatory, compulsory, or requisite would work best. Use any of these if there are some regulations or guidelines affecting the issue. But I don't think that's what you're going for.
If you're set on keeping the in-/im- prefix try integral (for the feeling of a much needed component) or imperative (for a feeling of urgency/necessity that has come from a command). There's also inflexible and immoveable, but those can be kind of clunky sounding.
Working with this constraint:
The word I'm thinking of sounds something like "invaluable" or "inviable"
I think the word you're looking for may be invariant or invariable, although both words don't feel entirely natural to me in your example sentence.
Another option: Obligatory - A single word which describing something that must be included/cannot be left out, either because some authority insists on it, or because of a social convention, more, etc. Something can be obligatory because it is required by law or rule, but it can also be obligatory because it is expected to such a degree that it would be socially or politically unacceptable not to include it.
I didn't go to Ned's pool party because I didn't have the obligatory beer hat.
Compulsory is similar, but with more connotations of an official or legal requirement.
You didn't mention the register the word you're looking for must belong to. If you're being informal, for keeps might work. The Collins English Dictionary defines as follows:
Something that is for keeps is permanent and will not change.
A bunch of examples from Longman Dictionary:
Marriage ought to be for keeps.
He's given it to me for keeps.
The specific word that you have in mind but have forgotten might be irreversible:
Not able to be undone or altered.
She suffered irreversible damage to her health.
It all depends on context, of course, but "unchangeable" ("not able to be altered," which could also be "unalterable") is understandable and precise.
I think "sacrosanct" is a great answer for the context given in the question. But it does have a religious or moral connotation. Then again, we're talking about a human hierarchy and authority (a CEO's preference), so it's not a purely technical scenario. Contrast that with the orbit of a planet governed by laws of physics, which I would not say are "sacrosanct" but could be called "unchangeable" or "inviolable."