TWTS: The honcho is already the head
The phrase "head honcho" is used to refer to people at the top: CEOs, presidents, directors and such.
However, "honcho" on its own means "leader." In other words, the head of something. That means, as is often the case in English, this commonly used phrase is redundant.
"Honcho" comes into English from Japanese in the 1940s. It originated around American prisoners of war in Japan. In Japanese, a "honcho" is a group leader or squad leader. American soldiers continued to use "honcho" during the Korean War. It comes into common usage in the U.S. in the 1960s.
The question remains, why do we have "head" in front of "honcho"? If the honcho is already the leader, it's redundant to say "head honcho." There's a chance that since "honcho" came in as a borrowing, "head" got tacked on to clarify its meaning.
"Head honcho" is used fairly commonly, but lately its popularity seems to be dropping off a little. Professor Anne Curzan says it could be that people aren't sure of its origin and whether it's offensive.
Regardless, it's not like we don't have plenty of other ways to talk about someone in charge or at the top. There's big fish, big cheese, top dog, big wig – take your pick.
For more on the story behind “head honcho,” check out Lakshmi Gandhi’s awesome article on NPR’s Code Switch blog.