first wave; first group
Used for the initial contingent of people or things arriving or departing, especially in military, immigration, or organized movement contexts.
The first wave of troops departed before dawn.
The first group of immigrants is scheduled to arrive next month.
Compound of 第一 (first) and 陣 (camp, battle formation, group). The exact historical derivation is uncertain, but the word follows a common pattern for numbering groups or waves.