To make dissatisfied or sulky; put out of humor. [from the prefix dis- (meaning "not") + gruntle, an obsolete word that intensified the meaning and impact of "grunt"] -- Funk & Wagnall's Canadian College Dictionary and The Oxford English Reference Dictionary
In other words, disgruntle means to "not gruntle," which for me instantly raised the question, "What, then, does 'gruntle' mean?" So here you go. I found the definition and a couple of delightful uses of "gruntle" online and discovered that it means "to put in a good humor." (from www.merriam-webster.com/dictionary/gruntle). Texan Walter Prescott Webb, 1888-1963, wrote that some people "were gruntled with a good meal and good conversation."
In the entry from the 1913 edition of Webster's Revised Unabridged Dictionary (found on www.thefreedictionary.com/gruntle), I learned that gruntle also once meant "to grunt repeatedly."
Then maybe another astute soul noticed that sometimes humans also grunt with pleasure at dinner time (and other pleasurable events) and applied "gruntle" to their expressions, too. Hence, over time, to be gruntled could come to mean that a person was in a good humor or tranquil.
Then, life being what it is, someone who was not in a good humor, was not feeling at ease and serene, might have come to be described as being "disgruntled." And, sad to say, the delightful little word gruntle passed from our daily vocabulary.
Personally, I'm really glad I found the word gruntle, because as it happens, earlier today I was feeling decidedly disgruntled about a variety of frustrations. However, it was time to write a blog post so I decided to investigate a Word Wonder. Those are usually entertaining for me, and I was hoping I'd get distracted from my grumpiness.
It worked. Not only did I get distracted, I got gruntled in my search for meaning...of the word "disgruntled." And the word "gruntled" is so charming and rolls so nicely around in my mouth, that I think it might just help me choose being gruntled over being disgruntled the next time I'm out of sorts. And, that, my friends, is an important part of healing and personal growth.