Eye of Newt

Ever get the feeling that you’ve come across a word before, but can’t remember where?

Definition of newt
any of various small salamanders that are usually semiaquatic as adults

and here’s how Shakespeare used newt in Macbeth:
second witch:
    Fillet of a fenny snake,
    In the cauldron boil and bake;
    Eye of newt and toe of frog,
    Wool of bat and tongue of dog,
    Adder's fork and blind-worm's sting,
    Lizard's leg and howlet's wing,
    For a charm of powerful trouble,
    Like a hell-broth boil and bubble.
   
translation--
second witch:
    Fillet of a snake that lived in a bog,
    In the cauldron boil and bake;
    Eye of newt, and toe of frog,
    Wool of bat, and tongue of dog,
    A black snake’s forked tongue, and its cousin’s sting,
    Lizard's leg, and owlet's wing,
    For a charm of powerful trouble,
    Like a hell-broth, boil and bubble.

ALL:
    Double, double, toil and trouble;
    Fire burn and cauldron bubble.