第一線|だいいっせんdaiissen[1]atamadaka (head-high)

1. nounthe front (of a battlefield); forefront
   彼女かのじょは今いまも第一線だいいっせんで活躍かつやくしている。↗

   She's still active in the front lines.

• Synonym最前線さいぜんせんNeutralThe frontmost battle line or the cutting edge of research and development, as in 「研究の最前線」; 「第一線」 stresses being active on the front line.
• Related先頭せんとうNeutralThe very front of a line or the lead, as in 「先頭に立つ」; 「第一線」 suggests an active front-line post in battle or a profession.
• Related陣頭じんとうWrittenWritten/formal prose: the head of a troop column or personal command, as in 「陣頭指揮」; 「第一線」 refers to front-line posts.
• Antonym後方こうほうNeutralThe rear or back; contrasts with 「第一線」 as the rear to the front line.

Use 「第一線」 for an active front-line position in battle or a profession, as in 「第一線で活躍する」「第一線を退く」. Pick 「先頭」 for the head of a line, 「最前線」 for the very front or cutting edge, 「陣頭」 for personal command, and 「後方」 for the rear.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

1. 戦場せんじょうで、最もっとも前まえにある敵てきと直接ちょくせつ戦たたかう場所ばしょ。