To feel envy or be jealous of someone else's possessions or situation (used as 'to envy X').
友達の昇進を羨んでしまったが、すぐにお祝いを言った。
I felt jealous of my friend's promotion, but I soon congratulated them.
あの人の才能を羨むより、自分にできることを増やそう。
Instead of envying that person's talent, try to increase what you can do yourself.
子供は友達が新しいおもちゃを持っているのを羨んだ。
The child envied that a friend had a new toy.
彼は他人の成功を見て深く羨んだが、それが努力の原動力にもなった。
He deeply envied others' success, but that also became a driving force for his effort.