coot

noun3

1. •
   Any of various aquatic birds of the genus Fulica that are mainly black with a prominent frontal shield on the forehead.
2. •
   (informal) A foolish or eccentric fellow

   • Once more he thought aloud. / "Tom wouldn't lie to me, so it wasn't gin. Now, I wonder. I wonder if that old coot has got what they call 'delusions of grandeur'?" — 1918
3. •
   (slang) Body louse (Pediculus humanus).