To make content or satisfied; the opposite of disgruntled (though rarely used as a positive standalone verb).
From Old English "gruntettan," the same root as grunt, but used in an archaic sense meaning to put in good humor. The prefix dis- (meaning not) was added to create disgruntled, which became so common it eclipsed the original.
Gruntle almost disappeared from English entirely—but it's become a cult favorite among linguists and word nerds because it's the rare word that's more famous in its negated form (disgruntled) than on its own, making it a linguistic paradox.
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