Gasser - 1. Something that is extraordinarily pleasing or successful, especially a very funny joke. 2. A person or thing that gasses.
Neville Longbottom had never thought of himself as particularly clever or successful. He'd been late performing his first magic; he was consistently bottom of the class; he'd never been good enough to live up to his Grandmother's expectations.
But, when Dumbledore gave him what were very nearly his first ever points for Gryffindor, he won them the House Cup.
There was a moment of silence and then everyone around him screamed with joy. They leapt on him, hugging him as hard as they could even as they deafened him.
In that instant, Neville knew what it was to be successful.