The fact is Geronimo is not an Indian name. It's Spanish, and it's the Spanish form of the name Jerome.
The famous Apache warrior and chief (pictured above) was given the Spanish name Geronimo (also spelled Jeronimo in Spanish) by Americans who heard Mexican soldiers scream "San Jeronimo!" (Saint Jerome!) when they were fighting the Apaches. They thought that was the Apache chief's name.
Sometimes Chamorros will have Spanish names that are unfamiliar to us, and which sound like something else but with no real connection. An example of this is the male name Froilan, a name some Chamorros had (and some still do). There was a Spanish saint by the name of Froilan, but it sounds similar to the German word "fraulein" or "miss" (unmarried woman). So, some people think Froilan is a German name.