[Anahki]

There are dozens of different examples of both, in completely different scenarios. It is something like "what is a werewolf?", but with less examples.
The original lamia was a monster, a woman with serpent body instead of legs who ate humans, from the greek mythoiogy. About the original nagas I am not sure, but I suppose they come from Indian mythology, and they were a rece of reptilian people.
After that, they have been depicted in many different ways, in literature, paintings, video games, movies, etc.