The odd item from the options listed is "Sonnet." A sonnet is a type of poem that traditionally consists of 14 lines, while the other options are all prose genres. Romance, novel, and short story are all forms of prose narrative that convey stories through characters, plot, and setting, while sonnets typically express a single idea or emotion in a structured poetic form. Therefore, the odd item is "Sonnet" as it does not belong to the category of prose genres.