Dewan was a language derived from the ancient Iconian language, with which it shared certain similarities, presenting the hypothesis that some Iconians were able to survive the orbital bombardment of Iconia. (TNG: "Contagion")
In the video game Star Trek Online, the Dewans (β) were an extinct pre-warp civilization native to Dewa III (β). Their homeworld was once an Iconian colony before the Iconians had to flee the planet during the war that destroyed the Iconian civilization. 50,000 years later, the Dewans found an abandoned Iconian gateway on their homeworld and attempted to activate it, unaware that the gateway's geothermal power source had been damaged during an orbital bombardment. This caused massive earthquakes and volcanic eruptions all over the planet, which ultimately drove the Dewans into extinction.