For the act of applying:
* Application: This is the most common noun and can be used in many contexts.
* Submission: This is used when referring to applying for something like a job or a loan.
* Request: This is used when referring to applying for permission or a service.
* Usage: This refers to the application of something, like a rule or a principle.
For the thing applied:
* Coat: This refers to a layer of something applied to a surface.
* Treatment: This is used for medical applications or treatments.
* Solution: This refers to a liquid or substance applied to a problem.
Other options:
* Implementation: This refers to the process of putting something into action or practice.
* Utilization: This refers to the practical use or application of something.
Examples:
* "I submitted my application for the job."
* "The treatment for the infection was very effective."
* "They need to apply a new coat of paint to the house."
* "The company is implementing a new solution to improve efficiency."
The best noun to use depends on the specific context and what you want to emphasize.