Which figure of speech is used in this text?
Isabella asked her mother if she could adopt a cat, and her mother replied, "It's a definite maybe," so Isabella didn't want to get her hopes up.

 - euphemism
 - oxymoron
The text uses an oxymoron, a joining of two seemingly contradictory terms.
Definite maybe is a contradiction, because definite describes something that is sure, and maybe refers to something that is unsure.