from The American Heritage® Dictionary of the English Language, 4th Edition
- pro. Used to indicate a reciprocal relationship or reciprocal actions among the members of the set referred to by the antecedent, often with the implication that the actions are temporally ordered: The students help one another. The waiters followed one another into the room. See Usage Note at each other.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- pro. Used of a reciprocal relationship among a group of two or more people or things; compare each other.
Sorry, no etymologies found.