The key word for Jaroslav Halak is “fun.”

He didn’t have much fun in 2015-16 with the Islanders. He was injured in training camp, then twice more during the season, with the groin injury he suffered late in the third period against the Penguins on March 3 ending his season after only 36 games, down from 59 the season before.

After watching Thomas Greiss lift the team to a playoff series win, Halak had hernia surgery in May, throwing his Islanders future into even more doubt.

But he must have said that word “fun’’ a dozen times on Monday while describing his experience for Team Europe at the just-concluded World Cup in Toronto. Halak, named the starter when Frederik Andersen was ruled out with a shoulder injury, ended up being one of the four or five best players in the tournament. He played more minutes (362) than any other goaltender and carried Europe to within a few minutes of a deciding third game in the best-of-three finals against Canada.

Monday was Halak’s first full day back with the Islanders and he’ll take the ice Tuesday. He might get only one preseason game before the Isles open the regular season against the Rangers on Oct. 13, but two things seem certain: Halak doesn’t need the work and he’ll be between the pipes at Madison Square Garden for the opener, having cemented his No. 1 spot with his impressive World Cup.

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“I just want to get out there, feel the puck and have fun,” he said. “Being injured a lot last year, I just want to enjoy it. That’s what we all want from when we’re young kids to now, just to have fun playing. Everything worked out well for me. Obviously you don’t want to see [Andersen] go down, but it was a chance for me and it worked out. The first game being back felt kind of weird, exactly six months since the injury, but I enjoyed it. I enjoyed every minute of it.”

Greiss, who played part of one Team Europe pre-tournament game but was in street clothes for the rest, returned to Long Island over the weekend and made his preseason debut on Monday against the Devils at Barclays Center.

“Just trying to get ready as much as I could in practice even though I didn’t play very much,” Greiss said of his World Cup experience. “A lot of good players to practice with, so it was good to have that. You want to play a few games quick [here], get back in the groove.”

Despite Greiss’ career season last year and excellent playoff performance, he seems unfazed as usual about his role to come as well as of Halak’s re-emergence during the past month.

“It’s great,” Greiss said. “Whatever helps the team, it can only help us as a group and make us better.”

Notes & quotes: Greiss played the full game Monday night and made 22 saves in a 4-3 Islanders win. Colin Markison, Andrew Ladd, Stephen Gionta and Mathew Barzal had the Islanders’ goals. They host the Rangers on Tuesday night.