noun
duplicity; treachery; double-dealing
Refers to having a divided heart or disloyal intentions; often used in literary or formal contexts to describe betrayal or faithlessness.
彼の二心を見抜けなかった自分が悔しい。
I regret that I couldn't see through his duplicity.
二心を抱く者は信頼されない。
Those who harbor treachery are not trusted.