Translation

敵対者 / 対抗者 / 相手

Meaning

An adversary is a person, group, or force that opposes you in a conflict, contest, or serious dispute. It is more formal and stronger than opponent.

Examples

• その弁護士は手ごわい相手として知られていました。
  The lawyer was known as a formidable adversary.
• その会社は、小さな新興企業を深刻な競争相手と見なし始めました。
  The company began to see the startup as a serious adversary.