What is the antonym of mouth?

There isn't a single perfect antonym for "mouth" because it has multiple meanings. Here are some possibilities depending on the context:

For the opening in the face:

* Nose: This is a direct contrast, being the other prominent opening on the face.

* Ear: Another contrasting facial opening.

* Eye: While not technically an opening, it is another sensory organ on the face.

For the act of speaking:

* Silence: The absence of speech.

* Writing: A different form of communication.

* Thinking: The process of formulating ideas without expressing them verbally.

For the opening of a container or object:

* Closure: The opposite of opening.

* Lid: A physical barrier that covers an opening.

For the entrance or outlet of a river:

* Source: The origin of the river, the opposite of its outlet.

To choose the best antonym, consider the specific meaning of "mouth" in your context.