Relational Model Design - Entity with one attribute

I am trying to design a database relational model for an assignment. First, I design the ER diagram, and then the relational model with tables (schemas). Here's my question: Is it possible for an entity to have only one attribute? To put a bit more to this: is it possible or logical to come to a relation with a single attribute in the course of decomposition? If that happens, and is accepted, how should one proceed?