一心|いっしんisshin[3]nakadaka (mid-high)

1. adverb, nounone mind
2. adverb, nounwholeheartedness; one's whole heart

• Synonym専念せんねんNeutralDevoting yourself to one thing only, as in 「研究に専念する」. 「一心」 stresses a mind free of distractions and is mostly adverbial, as in 「一心に」.
• Synonym傾注けいちゅうWrittenWritten/formal prose: pouring energy into something, as in 「全力を傾注する」; the stress is on effort invested, while 「一心」 stresses single-mindedness of heart.
• Synonym専心せんしんWrittenWritten/formal prose: concentrating on something, as in 「学業に専心する」; more solemn than 「専念」. 「一心」 can also mean hearts united as one.
• Synonym一心不乱いっしんふらんNeutralA four-character idiom meaning wholehearted single-mindedness, as in 「一心不乱に祈る」; stresses being completely undistracted.
• Synonym集中しゅうちゅうNeutralThe most general word: concentrating, as in 「集中力」 or 「勉強に集中する」; also used for people or things gathering in one place.
• Synonym夢中むちゅうNeutralBeing absorbed or crazy about something, as in 「ゲームに夢中になる」; the point is fascination that makes you forget everything else, while 「一心」 is deliberate focus.
• Synonym没入ぼつにゅうWrittenWritten/formal prose: being immersed in something, as in 「作品世界に没入する」; stresses total absorption in it. In everyday speech 「没頭」 is more common.
• SynonymコンセントレーションNeutralA loanword for concentration, as in 「コンセントレーションを高める」; used mostly in sports.
• Antonym二心ふたごころNeutralA disloyal or doubting heart, as in 「二心を抱く」; the opposite of 「一心」 in the sense of united hearts with no treachery.

Use 「一心」 for focusing on one thing, as in 「一心に祈る」, and for hearts united as one, as in 「一心同体」. For devoting yourself to a task say 「専念」, in daily speech 「集中」, for being absorbed 「夢中」. The opposite is 「二心」.

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

1. 複数ふくすうの人ひとの心こころが一致いっちすること。
2. 一ひとつの物事ものごとに心こころを集中しゅうちゅうすること。