一いっ周しゅう年ねん

い

っ

しゅ

う

ね

ん

Meanings

1

one full year; first anniversary

Used to mark the completion of one year since an event, often in formal or commemorative contexts.

震しん災さいから一いっ周しゅう年ねんの追つい悼とう式しきが行おこなわれた。

A memorial service was held on the first anniversary of the earthquake disaster.

〈事こと〉の一いっ周しゅう年ねんを迎むかえるto reach the first anniversary of something
この店みせは来らい月げつ、開かい店てん一いっ周しゅう年ねんを迎むかえる。
This shop will reach its first anniversary of opening next month.
一いっ周しゅう年ねんを祝いわうto celebrate a first anniversary
会かい社しゃの一いっ周しゅう年ねんを祝いわうパーティーを開ひらいた。
We held a party to celebrate the company's first anniversary.

周しゅう年ねんN1
周年 is the general term for 'anniversary' used with any number (二周年, 十周年), while 一周年 specifically means the first anniversary.
記き念ねん日びN3
記念日 refers broadly to any commemorative date (wedding day, founding day, etc.), whereas 一周年 specifically marks the one-year mark since an event.

誕たん生じょう日びN5
誕生日 means 'birthday,' the anniversary of someone's birth, while 一周年 refers to the first anniversary of any event, not necessarily a birth.

Compound of 一 (one) + 周年 (full year, anniversary). The reading いっしゅうねん follows standard rendaku and gemination rules.