Actually, it is not as categorical as implied in your question. Gossip is, at the very best, a waste of precious time, and at the very worst, character assasination.
What you report here is a charming homily -- an exaggerated statement to drive home how horrible gossip is. But to say that it is really the same type of sin as murder? Well ... that is a bit of a stretch.
The concept you are asking about is called ‘lashon hara’ [covering the areas of gossip, slander, and tale-bearing]. Literally It translates as the evil tongue, or more colloquially, evil speech. There are numerous and extensive discussions of this topic. One of the foremost Jewish authors in this area is called the Chofetz Chaim (Desirer or Seeker of Life) after the title of his book on this topic, taken from Psalm 34:12-15. The actual name of the author was Rabbi Israel Meir Kagan.