gruntle

grunt +‎ -le (early modern English frequentative suffix)

gruntle (third-person singular simple present gruntles, present participle gruntling, simple past and past participle gruntled)

1. (obsolete) To utter small, low grunts.
2. (obsolete) To complain; to grumble

From grunt +‎ -le (diminutive suffix).

gruntle (plural gruntles)

1. A grunting sound.
2. A snort.

Back-formation from disgruntled.

gruntle (third-person singular simple present gruntles, present participle gruntling, simple past and past participle gruntled)

1. (humorous) To humour; to induce the opposite effect of causing a person to become disgruntled.

   Synonyms: humour, regruntle (humorous)

To gruntle is not in normal usage. It has gained a certain currency amongst information security specialists to describe a process whereby the negative feelings of a disgruntled user might be reduced, or positive feelings induced.