What word is used to describe a phrase that uses antonyms for example Giant shrimp?

There isn't a single, universally accepted word to describe a phrase that uses antonyms. However, several terms could be used depending on the specific context and desired emphasis:

General terms:

* Oxymoron: This is the most common term and is generally used when the antonyms are juxtaposed, creating a paradoxical effect. While "Giant shrimp" doesn't quite fit the classic definition of an oxymoron (since shrimp are generally small), it could be considered one in a broader sense.

* Contradiction in terms: This phrase emphasizes the inherent logical inconsistency of the phrase.

* Paradoxical phrase: This term highlights the unexpected or surprising nature of the combination of antonyms.

More specific terms:

* Juxtaposition: This term refers to the placement of two contrasting elements side-by-side.

* Antithesis: This term specifically refers to a rhetorical device that uses contrasting ideas or words to create a strong effect.

* Irony: This term can be used if the phrase is intended to be humorous or sarcastic.

Ultimately, the best word to use will depend on the specific phrase and the context in which it is used.