• 肯定こうてい — affirmation; saying yes
• 肯定的こうていてき — positive; affirmative in tone
• 自己肯定じここうてい — self-acceptance; self-affirmation
• 首肯しゅこう — a nod of agreement; assent

With the “flesh/body” radical ⺼（にくづき）, 肯 shows a body that is firmly set, ready to accept. It came to mean giving a solid “yes” — acknowledging, approving, or being willing.