Final answer:
The Latin word for "king" that is also a male given name is Rex (option a). This word is historically significant due to Roman leaders' avoidance of the title to express their antipathy towards kingship after the Republic was established.
Step-by-step explanation:
The male given name that is also the Latin word for "king" is a) Rex.
The term Rex is deeply rooted in Roman history. Despite the eventual fall of the Roman Republic and the shift to a monarchical rule by kings in ancient Rome, the Roman leaders refrained from calling themselves Rex due to the Roman antipathy to kings. This illustrates the complexity of ancient Roman governance and the nuanced use of certain titles, even as the Principate period began where terms like "Caesar" came to signify the emperor.
Rome, named after its first king Romulus, witnessed the rise and fall of several kings until the Roman Republic was established and monarchy was forsaken. These historical events echo through the reluctance of later Roman leaders to assume the title Rex, thus honoring a longstanding tradition against tyranny and absolutism.