Parts of Speech: Noun, Verb, or Adjective?

work                              My husband works too much.

attendance                                         We take attendance everyday in class.

happy                                                  That is a very happy baby.

addition                                        Addition is the easiest part of mathematics.

additional                         There is an additional fee for returning the car a day late.

attend                                               Did you attend the party last Saturday?

work                                                It's a lot of work to take care of a child.

happiness                                          Many people are pursuing happiness in life.

popular                                           Taylor Swift is a popular singer.

Which isn't a noun ending?