The origin of the names of each follow a similar pattern. In each case, they originated from individuals who were promoting their own projects. It was only later that the terms became representative of genres with unique identities.
CyberpunkWhile Bruce Bethke doesn’t take credit for the creation of Cyberpunk genre, he correctly states that it originated with William Gibson who wrote the novel Neuromancer in 1984; he did create the term Cyberpunk, which was solely for bringing attention to the short story he had written. According to Bethke, "The invention of the c-word was a conscious and deliberate act of creation on my part. I wrote the story in the early spring of 1980, and from the very first draft, it was titled 'Cyberpunk.' In calling it that, I was actively trying to invent a new term that grokked the juxtaposition of punk attitudes and high technology. My reasons for doing so were purely selfish and market-driven: I wanted to give my story a snappy, one-word title that editors would remember.”
SteampunkThe name Steampunk originated in the same manner as Cyberpunk. The credit for coining the term ironically goes to one of the great Cyberpunk authors, K.W. Jeter. According to Cory Gross in an article published in Issue 2 of Steampunk Magazine titled, A History of Misapplied Technology, K.W. Jeter had written the following letter to Locus Magazine in 1987:
Enclosed is a copy of my 1979 novel Morlock Night; I'd appreciate your being so good as to route it Faren Miller, as it's a prime piece of evidence in the great debate as to who in ‘the Powers/Blaylock/Jeter fantasy triumvirate’ was writing in the ‘gonzo-historical manner’ first. Though of course, I did find her review in the March Locus to be quite flattering.
Personally, I think Victorian fantasies are going to be the next big thing, as long as we can come up with a fitting collective term for Powers, Blaylock and myself. Something based on the appropriate technology of the era; like ‘steampunks,’ perhaps...
In his article, Gross quoted Michael Berry who wrote for the San Francisco Chronicle in 1987:
Jeter, along with fellow novelists Tim Powers and James Blaylock, seems to be carving out a new sub-genre of science fiction with his new book. Whereas such authors as William Gibson, Michael Swanwick and Walter Jon Williams have explored the futuristic commingling of human being and computer in their 'cyberpunk' novels and stories, Jeter and his compatriots, whom he half-jokingly has dubbed 'steampunks,' are having a grand time creating wacko historical fantasies.
DieselpunkThis brings us to the origin of the term Dieselpunk. Lewis Pollak coined the term Dieselpunk for his role-playing game Children of the Sun. In a 2001 interview with GamingReport.com he stated, "Dieselpunk is the darker, dirtier side of steampunk. Think of a continuum between steampunk and cyberpunk. In terms of magic level, technological level, and grit/mood/tone, dieselpunk falls in between the two."
While it might be possible to argue that the Transhumanism Movement has the potential for being a Cyberpunk lifestyle, the term Cyberpunk never really went beyond being simply a descriptive term for a form of literary or cinematic science fiction. Only Steampunk and Dieselpunk have gone on to create unique sub-cultures with their own distinctive fashion, music, art as well as other features.