戦・軍・兵|いくさikusa[0]heiban (flat)

1. nounwar; battle; campaign; fight
   腹はらが減へっては戦いくさができぬ。↗

   An army travels on its stomach.
2. nountroops; forces

• Synonym合戦かっせんNeutralBattles between samurai of old; also used figuratively for contests, as in 「歌合戦」. Neutral in tone, while 「戦」 sounds archaic.
• Synonym交戦こうせんWrittenFormal term for two sides engaging in combat, as in 「交戦国」; more formal than 「戦」.
• Synonym戦争せんそうNeutralThe standard everyday word for war between nations; 「戦」 sounds archaic by comparison.
• Synonym戦闘せんとうNeutralConcrete fighting or combat operations, with emphasis on the exchange of fire; 「戦」 names warfare more broadly.
• Synonym戦役せんえきWrittenWritten word for a war or a campaign, as in 「日露戦役」; historical flavor. 「戦」 is likewise archaic.
• Related戦火せんかWrittenWritten word for the flames and ravages of war, as in 「戦火を逃れる」; stresses wartime destruction rather than the fighting itself.
• Related戦いたたかいNeutralA broad word for battles and struggles of every kind; common in daily speech, unlike the archaic 「戦」.
• Related軍ぐんNeutralThe army or armed forces, stressing the organization; it does not refer to warfare itself as 「戦」 does.
• Related衝突しょうとつNeutralA clash or collision, physical or figurative, as in 「武力衝突」; covers conflicts beyond warfare.
• Related軍勢ぐんぜいWrittenWritten, historical word for a force of troops or military strength, as in 「大軍勢」.
• Related修羅しゅらWrittenWritten word for carnage and bloody fighting; also the Asura demigod. Seen mostly in compounds like 「修羅場」, with a Buddhist coloring.
• Related争いあらそいNeutralQuarrels, disputes, and rivalry in general, not restricted to armed force as 「戦」 is.
• Related闘争とうそうWrittenWritten word for struggle, as in 「闘争心」; stresses fighting for a cause rather than warfare itself.
• Related奮闘ふんとうNeutralHard fighting or strenuous effort; the emphasis is on exertion, and war need not be involved.
• Related兵馬へいばWrittenWritten, archaic term for troops and horses or armaments; can also stand for warfare itself.
• Related干戈かんかWrittenLiterary word for arms and warfare, as in 「干戈を交える」.
• RelatedバトルNeutralLoanword for a battle, fight or head-to-head showdown; most at home in games and variety shows, with a modern feel far from the archaic 「戦」.

「戦」 is an archaic-flavored word for warfare or a battle, as in 「関ヶ原の戦」. For modern war choose 「戦争」, for combat 「戦闘」, for two sides engaging 「交戦」, for game showdowns 「バトル」, and for struggles 「闘争」. 「戦い」 is the everyday broad term; 「戦火」「戦役」「兵馬」「軍勢」「修羅」「干戈」 are written or historical; 「軍」 is the military organization; 「争い」「衝突」 cover non-armed conflict; 「合戦」 is old samurai battles; 「奮闘」 is hard effort.

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

1. （いくさ）敵対てきたいする集団しゅうだんが、現実げんじつに武力ぶりょくを行使こうししあう局面きょくめん。戦闘せんとう、会戦かいせん。