noun
first wave
Used for the initial wave of a phenomenon, such as an epidemic, attack, or trend. Often appears in news and analytical contexts.
新型コロナウイルスの第一波は2020年春に到来した。
The first wave of the novel coronavirus arrived in spring 2020.
敵の第一波の攻撃をなんとか防いだ。
We somehow repelled the enemy's first wave of attacks.
Compound of 第一 (first) and 波 (wave). The reading だいいっぱ follows regular rendaku voicing of は to ぱ after ん.