Etymology
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gruntle (v.)

1938, in gruntled "pleased, satisfied," a back-formation from disgruntled. The original verb (early 15c.) meant "to utter a little or low grunt," hence "to murmur, complain" (1560s), but was rare or dialectal by 18c.

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disgruntle (v.)

"disappoint, offend, throw into a state of sulky dissatisfaction," 1680s, from dis-, here probably meaning "entirely, very," + obsolete gruntle "to grumble, utter a low grunt" (Middle English gruntelen, early 15c.), frequentative of grunt (v.); hence "to complain" (by 1560s). All citations in OED are in the form of the past-participle adjective.

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