Sorry, but the question doesn't make any sense to me. Lots of things can contrast with idioms. It sounds as if your teacher had a list of words that they wanted you to contrast, and one was the opposite of idiom. We'd have to see the entire list to decide.
This isn't an idiom because you can figure it out if you look up the word "pins." It is a SLANG term meaning legs, so you knocked him over.
An idiom is a phrase that seems to be nonsense unless you know the definition. The word band's is the possessive of the word band, meaning "belonging to the band." It is a word, not an idiom.
Pest is not an idiom. It's a word.
My Favorite IDIOM Is, When Pigs Fly.
the idiom of really upset is "pissed off"
Madagascar is not an idiom, it is an island off the coast of Africa.
contrasts, differs...
An idiom is a phrase that cannot be defined literally. Nut is a word, not an idiom. It is a Germanic word.
No, an idiom is not a slang word. An idiom is a commonly used expression with a figurative meaning that is different from its literal meaning. Slang, on the other hand, refers to informal words and phrases that are specific to a particular group or generation.
moidi laciteopnuthis is french for un-poetical idiom
Prose
Idioms are phrases that cannot be defined literally - bush is a word, not an idiom. I'm not aware of any special significance of the word.