Barbule is a term used in ornithology to refer to the microscopic structures that make up bird feathers. While "barbule" is the only proper term to describe these structures, there are several synonyms that are often used in related fields of biology and zoology. Some of these synonyms include filoplume, pennaceous, plumule, and vane. These terms are often used interchangeably with barbule to describe the feather structures that help birds to fly and regulate their body temperature. While these words may not be commonly used in everyday conversation, they are important in scientific research and the study of avian biology.