Which word indicates that something is absolutely necessary?

The term "indispensable" conveys that something is absolutely necessary and cannot be done without. It emphasizes that the item or concept in question is essential for a particular function or situation; without it, the outcome is significantly compromised or unachievable. In various contexts, "indispensable" is often used to underline the importance of certain elements in processes, operations, or relationships, indicating that their absence would lead to failure or a breakdown.

While the other words—essential, critical, and vital—also suggest a high level of necessity, they might not carry the same weight or connotation of being completely unavoidable. For instance, "essential" refers to something that is necessary or fundamental, but it can imply that there are alternatives. "Critical" often relates to a situation that demands immediate attention or importance, and while it indicates urgency, it may not encompass the same level of certainty as being indispensable. "Vital" suggests something is necessary for life or fundamental functioning, but again, it could imply alternatives exist.

Thus, "indispensable" specifically captures the notion of something that one cannot afford to lose or do without, making it the strongest expression of absolute necessity in this context.