The answer to the blank is: figure.
A figure of speech or rhetorical figure is a phrase or word that makes use of figurative language (as opposed to literal language, figurative language deviates from the conventional meaning —the dictionary definition, for example— of a word in order to deepen the sense or meaning of the word by means of interpretation).
A figure of speech is meant to carry the expression further than its literal meaning by inventive means such as the ones that can be found in any metaphor or simile, like: your eyes are like diamonds.