There have been a lot of changes in the way people use hyphens (a dash is different; it's used within sentences - like this - to break them up.) Probably because of the huge number of new words entering the language, which are formed by combining old ones, there isn't time to think about rules, so they have been relaxed. So your example could really be "multichannel" or "multi-channel." It probably shouldn't be "multi channel" though, because "multi" is only a prefix and doesn't exist as a word in its own right. That rule is helpful - for instance, you can say "post office" not post-office, because post is actually a word. But you shouldn't really say "ex wife" because ex isn't a word (though according to some new dictionaries, it is. Like I said, rules are changing!)
You can find more information about the rules for using suffixes if you click here where they give a lot of detail about this.
You can find more information about the rules for using suffixes if you click here where they give a lot of detail about this.
