The name Mcarthur is a boy's name of Scottish origin meaning "son of Arthur". Mcarthur and discussed in our forums with posts like "Change two letters (5 names)".
From the experts:
The Mc and Mac surnames are asserting themselves as first names and this is one of the most popular. Though outside the U.S. Top 1000, it's among the fastest rising names for boys. And why not? McArthur or Mcarthur (or the Mac version of the name) makes a perfect honorific for an ancestral Arthur and leads directly to the nicknames Mac or Art.