I think the word you're looking for is "eddy" (sometimes spelled "eddie")
dyne
dash
The four letter word that means, "I forbid," is veto.veto
The four letter word is dawn.
Isle
A "bay" is a small protected body of water that is a four-letter word.
A four letter word for the noun brook is rill or a burn.
Exit
fern
slit
A Wren.
twig