Definitions
1.NounAn electronic message posted to multiple newsgroups or forums simultaneously.
2.NounAn instance of crossposting, or the post thus created.
3.VerbTo post (a message) to multiple newsgroups or forums simultaneously.
4.VerbTo post an entry (in a book index or other index) such that no matter which word a user looks under, they will find the relevant entry (see examples).