If a word is a verb:
1. It can be stated in the third person singular verb form:
2. It can be formed with an ing ending.
3. It can be used with a modal verb.
Example: Is the word dance a verb?
1. It can be used in third person singular: He dances so well.
2. It can be formed with an ing ending: The couple was dancing perfectly in the competition.
3. It can be used with a modal: They could dance all night, if they didn't have work in the morning.
The answer to all of these is 'yes'. The word 'dance' is a verb.