[Edited for clarity per feedback] I am creating a table of work items, and I want to label those items that are needed as other items are dependent on them. This label will be a different column. 'Dependency' is not clear as it could mean either way - this item is dependent on another OR another item is dependent on this. Whats the one word? Is 'Predecessor' the most apt or there's a better option?
Try "priority," which can be used as either a noun or adjective. While "priority" is often used to mean "important," it actually means that it comes first, i.e., prior to others that are to follow.
Another term you might try is "protasis" (noun) or "protatic" (adjective). The protasis is the if clause in an if-then sentence. Something is protatic when it is a condition or requirement for something else happening.
A third term that is both a noun and an adjective that you might try is widely used by universities for courses that must be taken before later courses: prerequisite. In the vernacular, that often gets shorthanded to "prereq." If you are required to take Math 423 - Quantitative Analysis to graduate but can't take that course until you've taken and passed Math 385 - Advanced Statistics, then Math 385 is a "prereq."