What feature is described as having a short, broad, bold head with a definite masculine appearance?

The description of a short, broad, bold head with a definite masculine appearance aligns strongly with the characteristics typically associated with a bulldog. Bulldogs are known for their distinctive head shape, which is wide and flattened, contributing to their robust and sturdy look. This feature is often considered representative of masculinity in the breed, making it a well-recognized trait.

In contrast, other options do not match the description. A butterfly is an insect with delicate features, lacking any comparison to the robust head described. A bullfrog, while it may have a broad appearance, has a very different head shape and overall body type characterized by its amphibian traits. Lastly, bullion refers to gold or silver in bulk rather than a physical animal characteristic, making it irrelevant in the context of this question. Thus, the bulldog is the distinct choice that accurately fits the provided description.