General:
* Requirement: This is the most common and direct noun for "require." It refers to something that is needed or essential.
* Need: This emphasizes the necessity of something.
* Demand: This implies a strong or urgent need.
* Necessity: This refers to something that is absolutely essential.
More specific:
* Obligation: This emphasizes a duty or responsibility.
* Condition: This refers to something that must be met.
* Prerequisite: This refers to something that is required before something else can happen.
* Specification: This refers to a detailed description of what is required.
Figurative:
* Call: This can be used metaphorically to describe a need or a demand.
The best noun to use will depend on the specific context of your sentence.
For example, you could say:
* "The job has a strict dress code requirement."
* "There is a need for more affordable housing."
* "The customer's demand for a refund was met."
* "The doctor emphasized the necessity of a healthy diet."
Think about what you want to convey, and choose the noun that best fits your meaning.