Is an alligator a crocodilian?
Yes, the American Alligator is a crocodilian.

American Alligator
A crocodilian is an alligator, crocodile, caiman, and a gharial.
Crocodilians are large, predatory, semi-aquatic reptiles.
Photographer: Martina Nicolls
Martina Nicolls: SIMILAR BUT DIFFERENT IN THE ANIMAL KINGDOM