Celtic Meaning: The name Ronan is a Celtic baby name. In Celtic the meaning of the name Ronan is: Oath. American Meaning: The name Ronan is an American baby name. In American the meaning of the name Ronan is: Oath.Irish Meaning: The name Ronan is an Irish baby name. In Irish the meaning of the name Ronan is: Little seal.SoulUrge Number: 7. Expression Number: 8. People with this name have a deep inner need for quiet, and a desire to understand and analyze the world they live in, and to learn the deeper truths.he name Ronan is a Celtic baby name. In Celtic the meaning of the name Ronan is: Oath. American Meaning: The name Ronan is an American baby name.