自己|じこjiko[1]atamadaka (head-high)

1. no-adjectiveself; oneself
   彼かれは自己じこを没却ぼっきゃくする男おとこではない。↗

   He knows how to assert himself.

• Synonym自身じしんNeutralRefers to the self itself and often attaches as a suffix, as in 「彼自身」; 「自己」 mostly appears in compounds like 「自己紹介」.
• Synonym自分じぶんNeutralThe most common everyday word for oneself; colloquial, whereas 「自己」 leans written and appears mostly in compounds.
• Synonym自分自身じぶんじしんNeutralRefers to the self itself; an emphatic form of 「自分」, common in everyday speech.
• Synonym自我じがWrittenA written/formal word for the ego or self, also for self-assertion, as in 「自我が強い」 (strong-willed, unbending); 「自己」 mostly forms compounds for the self itself.
• Synonym自らみずからWrittenRead おのずから, an adverb meaning naturally or of its own accord; read みずから, it means doing something oneself. Linked to 「自己」 only by the character 「自」.
• Related本人ほんにんNeutralMeans the person in question, as in 「本人確認」; used when speaking of that person from an outside standpoint.
• RelatedエゴNeutralLoanword for the ego or for selfishness, as in 「エゴが強い」; often carries a negative nuance.
• Related我われWrittenA written word with an archaic flavor for I or oneself, as in 「我を忘れる」.
• Antonym他者たしゃWrittenA written/formal word for other people; stands opposite 「自己」.

Use 「自己」 in written or formal contexts and in compounds like 「自己紹介」 and 「自己責任」. In everyday speech say 「自分」; for the person in question 「本人」; for the ego or self-assertion 「自我」; the opposite is 「他者」.

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

1. 自分自身じぶんじしん。