• 堅かたい — hard / solid / strict
• 堅実けんじつ — steady / reliable
• 堅固けんご — firm / solid
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• 堅持けんじ — firm adherence
• 堅調けんちょう — steady (e.g., market)
• 堅牢けんろう — robust / sturdy
• 手堅てがたい — dependable / sure
• 堅苦かたくるしい — stiff / overly formal

堅 pairs the earth radical 土 with the phonetic part (臤) to picture packed, compressed earth—the source of “hard,” “firm,” and by extension “steadfast” character.