A newt is a type of salamander in that it fulfills the basic requirements: its skin is thin, it breathes through gills until its lungs grow, and the adults can leave the water and walk among us as land-dwellers.
The biggest difference from other salamanders is that adult newts have flatter tails than most. This isn’t a big difference, we know, but it will have to do.
When a newt finally grows up and leaves the water with a working set of lungs equipped for a life on land, it’s called an eft. From then on, they return to the water only briefly to catch up with old friends, check the mail, and mate.
Adult newts are brightly colored and are poisonous to predators. We can only guess that this is why “eye of newt” is part of the witches’ recipe in act 4 of Shakespeare’s Macbeth (“Double, double toil and trouble; Fire burn and cauldron bubble”).