Lewis is entering the last season of a six-year, $118 million contract and could be a candidate for the NBA's amnesty clause, meaning he may not end up playing for the Hornets if New Orleans instead chooses to clear some salary cap space.
"We are rebuilding our team and this is one step in our new direction," Hornets general manager Dell Demps said. "This trade will provide an opportunity for our young players to develop and create flexibility to add to our core group moving forward."
Wizards President Ernie Grunfeld said of the deal, "Rashard unfortunately was injured while he was with us, and he didn't get an opportunity to show the kinds of things he was capable of doing… He had a very hefty buyout in his contract, and we elected to add a couple of players to the roster by using his contract."
Grunfeld said the Wizards would have had to pay a $13.7 million buyout.
New Orleans also received the 46th pick in this year's draft, which originally belonged to Dallas.
The Hornets, who are expected to take Kentucky star Anthony Davis with the top-overall draft pick and also have the 10th selection, did not have a second-round pick before the trade. Washington, meanwhile, has the third-overall pick and still has the second pick of the second round.
Grunfeld said the deal won't have any effect on the team's draft plans.
"We felt like we needed to add some veterans to the roster, and we were able to do that with this move… We get players that are good solid players and fill two needs for us," Grunfield said. "Instead of going into free agency to try to fill our needs, we did it through a trade."
Okafor has never lived up to being the second pick in the 2004 draft, but has averaged double figures in points (12.7) and rebounds (10.1) during his career. Last season, however, he averaged a career-low 9.9 points and 7.9 rebounds and missed time with a sore left knee.
Ariza averaged 10.8 points and 5.2 rebounds, but was deactivated for the last few weeks of the season while the Hornets, already well out of playoff contention, took a closer look at younger players on the roster.
Several of those younger players, including second-year swingman Al-Farouq Aminu, showed signs of improvement as the Hornets won eight of their final 13 games.
Grunfeld said Ariza and Wizards point guard John Wall, the No. 1 overall pick in the 2010 draft, played together in a pickup game in Los Angeles on Wednesday.
"We think we're a better team today than we were yesterday," Grunfeld said, "but we still have a lot of work ahead of us."