Disgruntled, like unkempt, discombobulate, and nondescript, is a part of a category of words with a “lost positive” – “one of those interesting negatives without a corresponding positive word” (Garner’s 806).
This fact has led to discussions in print and online about whether gruntled is a word.
In 1999, William Safire asked in his NY Times “On Language” column, “How come you don’t ever hear about gruntled employees? Those of us in the scandalmongering dodge rely heavily on ‘disgruntled former employees’ for leaks, tips and other often-slanderous leads.”
Safire quotes The Oxford English Dictionary (OED) which defines gruntle as “to grumble, murmur, complain” and provides a quote from a 1589 sermon by Robert Bruce: “It becomes us not to have our hearts here gruntling upon this earth.” But Joseph Piercy, in the vocabulary book A Word a Day, states that gruntle came from the grunt sounds made by animals, particularly pigs. Piercy provides an example from an early 14th century fantastical book, The Travels of John Mandeville, in which natives near the Garden of Eden look hideous and “gruntle like swine” – a source also noted by O’Conner and Kellerman on grammarphobia.com.
According to merriam-webster.com, the word disgruntle has been around since 1682 with the meaning “to make ill-humored or discontented,” similar to the earlier gruntle, “which is why gruntled wasn’t originally the opposite [false positive] of disgruntled.” Dis- is commonly a negative prefix (as in the words disability, disbar, discontent, dislike, disown). But in the case of disgruntle (and also discombobulate), dis- is an intensifying or amplifying prefix: dis- plus the older word gruntled (meaning “to grumble”). According to the OED’s definition, to “disgruntle” was “to put into sulky dissatisfaction or ill-humour; to chagrin, disgust” (qtd in grammarphobia.com).
Gruntled, notes merriam-webster.com, in the older sense of “to grumble” is now used only in British dialect. However, in the 20th-century, gruntled began appearing in an upbeat sense, meaning ‘”to put in a good humor” or “pleasing, satisfied, contented.” In what several sources call a “back formation” from disgruntle, the false positive gruntle is “born again” (OED, merriam-webster.com, New Fowler’s).
Many articles have credited with the first modern use of gruntled in print to P.G. Wodehouse, creator of Jeeves, in his 1938 book The Code of the Woosters: “If not actually disgruntled, he was far from being gruntled.” Though merriam-webster.com cites 1926 as the earliest use, no instance is given for it. Instead, this site and others provide an example from the 1931 W. P. Webb book The Great Plains: “They were gruntled with a good meal and good conversation.” Despite appearances of gruntled, the word is far from common and even MS Word marks it with the red squiggly “misspelling” underline.
FYI – Bryan A. Garner notes in his usage guide that “disgruntled complaints” is a common everyday expression, in which “an adjective logically modifies not the noun actually supplied, but an implied one.” This phenomenon is called hypallage, (also the transferred epithet), “a figure of speech in which the proper subject is displaced by what would logically be the object (if it were named directly).” For example, consider the line from Shakespeare’s Julius Caesar: “This was the most unkindest cut of all” (3.2.183). As Garner writes, “it was not the cut that was unkind, but rather the cutter [Brutus]. Hence the object has become the subject.” In our phrase it’s not the complaints that are disgruntled, but the complainers, like Safire’s disgruntled employees. Garner goes on to say that even though this figure of speech is generally harmless, there are purists who object to these “convenient” phrases, such as when saying “But the marker itself isn’t permanent, is it?” His response that such disgruntled complaints are by people “simply parading their own pedantry” (216-217).