• 適当てきとう — suitable / appropriate
• 適応てきおう — adaptation / compliance
• 快適かいてき — comfortable
• 適切てきせつ — appropriate / proper
• 適性てきせい — aptitude
• 不適ふてき — unsuitable

The left part of 適 includes 舌 (tongue), while the radical 辶 represents movement or progression. Together, they suggest “moving toward what is suitable” or “matching the right path.” The kanji is used both literally and metaphorically to express fitness, comfort, and suitability.

この靴くつは 私わたしに 適てきしています。
These shoes are a good fit for me.

彼かれは 新あたらしい 環境かんきょうに 適応てきおうできる 能力のうりょくがあります。
He has the ability to adapt to new environments.