What It Means
: to put in a good humor
How It's Used
“It was a crime of passion, Jan, not a disgruntled employee. Everyone here is extremely gruntled." — Michael Schur, The Office: The Negotiation (Season 3, episode 18), April 5, 2007
The verb disgruntle, meaning "to make ill-humored or discontented," has the familiar prefix dis-, but it isn't the dis- we know. Rather than meaning "to do the opposite of," the dis- in disgruntle is a rare version of the prefix that acts simply as an intensifier.
Disgruntle, which dates to the late 1600s, comes from this intensifying prefix and a now-archaic word gruntle, meaning "to grumble." The early 20th century writer who humorously coined the new gruntle by removing the dis- to form an antonym of disgruntle likely knew nothing about the original gruntle. And neither do most people today who choose the word gruntle (often humorously) to mean "to make happy."