1.
to become absorbed in; to be engrossed in
To become so focused on or fascinated by something that one loses awareness of everything else.
ゲームに夢中になる。
I get absorbed in games.
子どもたちは砂遊びに夢中になっていた。
The children were engrossed in playing in the sand.
読書に夢中になって、電車を乗り過ごしてしまった。
I got so absorbed in reading that I missed my train stop.
The pattern is ～に夢中になる, where に marks the object of fascination. 夢中 can also be used as a na-adjective: 夢中で走った (ran frantically). When used with で instead of に, it often conveys doing something desperately or without thinking, rather than being fascinated. The literal meaning of 夢中 is "in a dream," reflecting the idea of being so absorbed that reality fades away.