"Shovelhead" is a slang term that refers to a Harley-Davidson motorcycle engine. However, there are several synonyms that can be used to describe this type of engine. One of the most common terms is "panhead," which refers to the engine that preceded the shovelhead. Another synonym is "blockhead," which is a term that was used to describe the newer, improved version of the shovelhead - the evolution engine. Other slang terms that are sometimes used include "Shovel," "Big Twin," and "FX." Regardless of the term used, these engines are known for their distinctive sound and classic style, which has made them popular among motorcycle enthusiasts for decades.