godan verb (-mu), transitive verb
Dialectal (Kantō) verb for feeling envy or jealousy toward someone's success, possessions, or situation. Used in casual speech.
友達の新しい車をやっかんでいる。
I'm envious of my friend's new car.
彼は同僚の昇進
He became jealous of his colleague's promotion and stopped talking to him much.