A conceit is a highly elaborate and extended metaphor that compares two very dissimilar things. It often involves surprising or unconventional comparisons.
Related terms
Metaphor: A figure of speech that directly compares two unrelated things without using "like" or "as."
Simile: A figure of speech that compares two unrelated things using "like" or "as."
Extended metaphor: A metaphor that is developed over several lines or throughout an entire poem.