Some nouns, not all, have opposites.
Noun opposites are called antonyms. Examples:
There is no postie of a koala. Nouns generally do not have opposites.
Nouns don't have opposites.
Finger is a noun. Nouns don't have opposites or antonyms.
Meat is a noun. Nouns do not typically have opposites or antonnyms.
Names, as proper nouns, do not have opposites. The meaning of a name may have.
Nouns describing objects do not have opposites. "Unncumbered" is the opposite of "burdened" (if by luggage you mean something that is a burden)
There are no antonyms for nouns, but the word "sedan" might work.
There is no such thing. It makes sense to talk about opposites of simple properties (adjectives), such as "fast", "clever", etc.; in general, it doesn't make so much sense to talk about the opposites of objects (nouns).
Nouns do not have opposites; 'ecosystem' is a noun. Therefore, ecosystem does not have an opposite. If nouns don't have an opposite... well, "top" is the opposite of "bottom", and they are referring to locations, hence they are nouns.
There really isn't an opposite to a taco. A taco is a Mexican food, and there are mostly never opposites to nouns. Though, you could say that the opposite of a taco could be a hot dog.
Some words do not have opposites. Generally those that do have opposites are adjectives or adverbs (fast vs. slow, rich vs. poor). Nouns often do not have opposites (e.g. there is no opposite for apple, steak, wine bottle). Girl follows that case. A girl is not the opposite of a boy. A girl is a young female human being, a boy is a young male human being. They are only different in one of the adjectives used to describe them, this does not make them opposite.
fire and water are opposites