The difference is that cowardly is usually an adjective, while coward is almost always a noun. Hence:
That dog is a coward.
That cowardly dog runs at the sound of hooves.
I couldn't understand how "coward" is noun in "That dog is a coward.", let's take the word brave as example:
That dog is brave.
Is brave an adjective in this sentence? If yes, so why is "coward" noun in the same clause structure?
if "coward" word is a none in "That dog is a coward", Does it has any difference meaning than:
That dog is not brave.
Another question: Can we remove the article "a"? is this make it adjective? Does it still has the same meaning?