It is an adjective and means “can’t wait for”. It is used when you look forward to something and you wait a long time for it to happen.
It is similar to "待ち切れない". Check the difference between them.
最近、すごく寒い。春が待ち遠しい。
Saikin, sugoku samui. Haru ga machidooshii.
- Ken : Have you beaten that video game yet?
もう、あのゲームをクリアしたの?
Mou, ano ge-mu o kuria shita no? - Leo : Yes. It was really challenging.
うん。超難しかった。
Un. Cho muzukashikatta. - Ken : Really? Well done!
本当?さすが!
Hontou? Sasuga! - Leo : I thought that it’s going to take forever, though. Anyway, I’m really excited about the new game that’s coming out next week!
一生終わらないかと思ったけどね。とにかく、来週新作のゲームが発売されるのが待ち遠しいよ。
Isshou owaranai kato omotta kedo ne. Tonikaku, raisyu shinsaku no ge-mu ga hatsubai sareru noga machidooshii yo.
- Meg : Do you have any plans for the summer?
今年の夏は、何か予定はあるの?
Kotoshi no natsu wa, nanika yotei wa aru no? - Amy : I'd like to go see my boyfriend in Hong Kong if the government allows people to go abroad.
政府が海外渡航を許可してくれるなら、香港の彼氏に会いに行きたいな。
Seifu ga kaigai tokou o kyokashite kureru nara, honkon no kareshi ni ai ni iki tai na. - Meg : I see. How long has it been since you’ve seen each other?
そっか。どれくらい、彼と会っていないの?
Sokka. Dorekurai, kare to atte inai no? - Amy : It's been three months. I would’ve gone to Hong Kong now if the coronavirus infection hadn't spread.
3ヵ月経つよ。コロナウィルスの感染が拡大していなければ、今頃は香港に行っていたのに。
Sankagetsu tatsu yo. Koronawirusu no kansen ga kakudai shite ina kere ba, imagoro wa honkon ni itte ita noni. - Meg : I feel sorry to hear that. Once things settle down with the coronavirus, I hope you can visit him.
残念だったね。コロナウィルスに関する問題が落ち着いたら、彼に会い行けるといいね。
Zannen datta ne. Koronawirusu ni kansuru mondai ga ochitsuita ra, kare ni ai ni ikeru to ii ne. - Amy : Thank you. I'm looking forward to seeing him next time.
ありがとう。次に彼に会うのが待ち遠しいな。
Arigatou. Tsugi ni kare ni au noga machidooshii na.