foul, fowl

Foul or foul means disgusting, dirty, or spoiled--
What is that foul smell?
Even a rat won't foul its own nest.
Foul may mean against the rules or unfair, as in some sports--
The fourth foul ball makes an out, in baseball.
"Foul play" is an expression from the old detective novels, meaning crime--
The detective began to suspect foul play.

Fowl or fowl ( rhymes with foul ) means a chicken, a duck, or another bird that is commonly eaten, such as a turkey or pheasant--
The fowl in the barnyard made a lot of noise.
They liked to hunt wild fowl in the woods.
Chickens are the most common domestic fowl.

Now that you know that, you can say--
"The barnyard was foul with the mess made by the fowl."

Note--to "foul up" something means to make a mess of it, or to ruin it--
Be careful. Don't foul up, or the team will never let us forget it.
Something that is "fouled up" is ruined--
The old army word "snafu" is said to be an acronym for "situation normal, all fouled up".
"Fouling" means getting something dirty--
He never stops fouling his own nest.
 Note # 2--"foul language" means obscene language, cursing or swearing--
The student was sent to detention for his foul language.
Note # 3--a "fowler"  hunts fowl, such as geese or pheasants--
The fowler shot a duck and a partridge.
A "fowling piece" means a gun used for shooting fowl--
He kept his old fowling piece cleaned and oiled.