crosspost

Etymology
From.

Noun

 * 1)  An electronic message posted to multiple newsgroups or forums simultaneously.
 * 2)  An instance of crossposting, or the  thus created.

Verb

 * 1)   To post (a message) to multiple newsgroups or forums simultaneously.
 * 2)   To  an  (in a book  or other index) such that no matter which word a user looks under, they will find the relevant entry (see examples).