Some people—and not a few usage guides—insist that although you can be a staunch friend you stanch the flow of blood from a wound. But “staunch” has been a standard spelling for word with the latter meaning from its origin in the 14th century, and is today more popular than “stanch.”
The two words spelled “staunch” are logically related through a root meaning “watertight”: you are tight with your allies and friends, clinging firmly to them; and you close a wound tightly to halt the bleeding. Even people who write “stanch” often pronounce it “stawnch.”