Definition
A chondrichthian is an individual member of the class Chondrichthyes. If 'Chondrichthyes' is the whole group, then a 'chondrichthian' is a single fish within that group. Think of it as the difference between 'mammalia' (the mammal class) and 'mammal' (one animal, like a dog). So, a shark is a chondrichthian, just like a ray is a chondrichthian. They all share that cartilaginous skeleton that defines the group.