What is "swellhead"

Usage examples of "swellhead".

They enter a school, tattle round lies, play silly jokes behind some one by sneaking and cheating and get wrongly swellheaded when they finish the school thinking they have received an education.

Night had never been as good, though there were those who found him much less approachable offstage: getting swellheaded, they said, what with the royal command and all.