What is excommunication? what role did it play in the struggle between popes and kings?

Thank you for using the Jiskha Homework Help Forum. When you don't know the definition of a word, be sure to look it up in a good dictionary. Here's what the Online Dictionary has to say. Then think about it and what do YOU think it meant in the struggle between popes and kings?

Main Entry: ex·com·mu·ni·ca·tion
Pronunciation: -"myü-n&-'kA-sh&n
Function: noun
Date: 15th century
1 : an ecclesiastical censure depriving a person of the rights of church membership
2 : exclusion from fellowship in a group or community
- ex·com·mu·ni·ca·tive /-'myü-n&-"kA-tiv, -ni-k&t-/ adjective