• 自己じこ — self
• 自己紹介じこしょうかい — self-introduction
• 利己りこ — selfishness
• 利己主義りこしゅぎ — egoism

己 may trace to a coiled or curved form and later came to signify the personal self. It’s also the sixth of the Ten Heavenly Stems (十干), appearing in calendrical terms.