• 衛生えいせい — hygiene / sanitation
• 自衛じえい — self-defense
• 防衛ぼうえい — defense
• 守衛しゅえい — security guard
• 警衛けいえい — guard duty
• 衛兵えいへい — military guard

衛 combines the enclosure/patrol sense of 行（ぎょうがまえ）with the phonetic 韋, conveying guarding or defending an area — extended in modern usage to protecting health, safety, and order.