What do we call a fanciful expression, typically an extended metaphor between dissimilar objects?

A fanciful expression that typically functions as an extended metaphor between dissimilar objects is referred to as a conceit. This literary device is characterized by its imaginative association and often surprising comparisons that invite readers to examine relationships between seemingly unrelated things. Conceits often go beyond typical metaphors or similes, creating an elaborate and sometimes complex connection that enhances the meaning or themes within a work.

For instance, in poetry, a poet might compare love to a ship at sea, detailing the intricacies of both experiences in a way that unfolds a deeper significance. This inventive engagement invites a deeper consideration of emotions or concepts, expanding the reader's understanding.

Other options include metonymy, which involves substituting the name of one thing with the name of something closely associated; allegory, which refers to a narrative that conveys a deeper meaning or moral often through symbolic figures; and symbolism, where an object or action represents a larger idea or concept. While these terms employ figurative language, they do not convey the same fanciful and extensive comparisons that define conceits.