Should Entity Name Be Singular or Plural?

So with databases, the entity when made into a table (a collection of entities or records) is plural. Entity, User is made into table Users. I would agree with others who suggested maybe the name User could be improved to Employee or something more applicable to your scenario.

Can entities be plural?

The plural form of entity is entities.

Should database names be plural?

It's a pretty established convention that database table names, in SQL at least, should be singular. SELECT * FROM user; See this question and discussion. It's also a pretty established convention that RESTful API resource names should be plural. GET /users/123 and POST /users See this one.