noun
first battle; first campaign; debut fight
Originally a military term for a warrior's first battle; now also used figuratively for one's first attempt at any challenging endeavor, such as a competition, exam, or new job.
彼は初陣で見事な勝利を収めた。
He achieved a splendid victory in his first battle.
新人選手の初陣
The rookie player's debut match is next week.