You could say imperative in a more formal situation. More on reddit.com

They are not all exactly the same, no. Crucial and Indispensable mean something that you can't do without, so they are stronger than just important. They also have slightly different collocations and connotations, so we tend to use them in different contexts. Indispensable is usually applied to people or objects, whereas crucial tends to be applied more broadly, including to more abstract things like ideas or events. Note that these are both only tendencies, though. Anything that is absolutely needed can be described with either word. Prominent is the least similar. It literally means something that sticks out, like a chimney from a roof. Metaphorically, and more commonly, it means something that is noticeable, often because it is important. It's frequently used for important people, like "a prominent member of the community" or "a prominent businessman". More on reddit.com

Integral?

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Be careful with synonyms!!! Sometimes the meanings are not exactly the same, or they have a different feeling to them that's hard to describe - and it can lead to misunderstandings or cause problems if you pick a synonym that has additional meanings you aren't aware of. For example, "mammoth" can be a synonym for "big," but it has more of an intensity to it and conjures up a mental image of the wooly mammoth, so you could say someone has a big smile but you wouldn't usually say they have a mammoth smile. I recommend checking out wiktionary.com to see synonyms but also get an idea of what extra senses those synonyms have. Usually there will also be a translation for the English word to your language! More on reddit.com