What is defined as expressing one's meaning by language that signifies the opposite?

The correct answer identifies a specific linguistic technique known as irony. This technique involves conveying a message in a manner that signifies the opposite of what is literally stated, often for humorous or emphatic effect. Ironic expressions play with the expectations of the audience, creating a layer of meaning that goes beyond the surface level of words.

For instance, if someone were to look out at a raining day and state, "What beautiful weather we're having," they are not merely making a benign statement about the weather but rather implying the opposite – that the weather is, in fact, unpleasant. This interplay between literal and intended meaning is a hallmark of irony.

In contrast, the other choices refer to different literary concepts. A metaphor involves a direct comparison between two unrelated things without using "like" or "as," aiming to create a symbolic understanding rather than conveying oppositional meaning. Allegory is a narrative technique where characters or events symbolize deeper moral or political meanings, while symbolism uses symbols to represent larger ideas or concepts, again not necessarily engaging with oppositional sentiment.

Understanding these distinctions clarifies why ironic expression is the most fitting definition for the concept of communicating meaning by signifying the opposite.