Explanation:

- Aquatic: This word is correctly spelled. It refers to things related to water.

- Notorious: This is the correct spelling. It describes someone or something famous for a bad quality or deed.

- Centinarian: ? This is incorrectly spelled. The correct word is Centenarian, which refers to a person who is one hundred years old or more.

- Mercenary: This word is spelled correctly. It refers to someone who is motivated by personal gain, typically a professional soldier hired to serve in a foreign army.