• 健康けんこう — health
• 健在けんざい — in good health
• 健児けんじ — robust youth
• 健勝けんしょう — good health (polite)
• 健全けんぜん — soundness / wholesomeness
• 健やかすこやか — healthy / vigorous

This kanji combines the person radical 亻 with the phonetic 建 (build/establish), suggesting a person who is “well-built” or sound—hence healthy and vigorous. It appears in words related to physical health, wellness, and soundness.