The verb "disgruntle," which has been around since 1682, means "to make ill-humored or discontented." The prefix "dis-" often means "to do the opposite of," so people might naturally assume that if there is a "disgruntle," there must have first been a "gruntle" with exactly the opposite meaning. But actually, "dis-" doesn’t always work that way — in some rare cases it functions instead as an intensifier. "Disgruntle" developed from this intensifying sense of "dis-" plus "gruntle," an old word meaning "to grumble." In the 1920s, a writer humorously used "gruntle" to mean "to make happy" — in other words, as an antonym of "disgruntle." The use caught on. At first "gruntle" was used only in humorous ways, but people eventually began to use it seriously as well.