To tattletale is to tell a tale about someone, one that's true, but one that may get the person into trouble. Children tattletale on each other. For example, Mom, Max didn't do his homework; Dad, Sam ate the goldfish; Teacher, Pat punched me. Children tattletale for various reasons; they feel it's their duty to be honest with authority, they feel it's unfair that the other person is getting away with something, etc. Adults tattletale, too, but it's not called that. It's called "not minding your own business", and it can have a negative result.
A gossipmonger is someone who perpetuates, or rather, sells (=monger) gossip. The gossip may or may not have some truth to it. That's what differentiates it from 'tattletale'. (Note, gossipmonger isn't as commonly used as is 'gossip'; e.g., S/he is a gossip; Adjective, S/he is so gossipy.)
To push the envelope comes from mathmatics. It means to push the limits of something so as to determine its true capabilities. Click here: