• 善良ぜんりょう — good-natured, virtuous
• 善意ぜんい — goodwill, good intentions
• 改善かいぜん — improvement
• 最善さいぜん — the very best
• 善行ぜんこう — good deeds

善 combines the elements 羊 (sheep) and 言 (speech). Sheep have long been a symbol of goodness or purity in East Asia, and 言 means speech or words. Together, they reflect "good words" or "virtuous expression" — a symbol of moral excellence.

彼かれは 善良ぜんりょうな人ひとです。
He is a kind and good-hearted person.

善意ぜんいで やったことです。
I did it with good intentions.

ゼン is the on-yomi and used in almost all words like 善意, 善行, or 善良. The kun-yomi よい is rarely used independently and appears in archaic or classical usage.