noun
adversary party; opposing party
Formal legal term used in litigation, arbitration, or contractual contexts to refer to the other side.
相手方当事者は、この契約の解除を求めた。
The opposing party sought termination of this contract.
裁判で相手方当事者の主張を聞く。
We hear the adversary party's argument in court.
Compound of 相手方 (あいてがた, 'the other side') and 当事者 (とうじしゃ, 'party concerned'). A formal legal term.