This is the 1395th most frequent Japanese word.
参戦
"参戦" means "participation in a war or battle."
The word '参戦' refers to actively participating in a conflict or war.
彼はその戦争に参戦しました。
He joined that war.
Here, '参戦' is used metaphorically to mean starting to participate in a competitive context, such as a game.
新しいオンラインゲームに参戦するつもりです。
I plan to join the new online game.
In this case, '参戦' connotes taking part in a heated or active exchange or debate.