suru verb (irregular), intransitive verb
side with; support; take part in
Used when someone aligns themselves with a person, faction, or plan, often in a dispute or undertaking. Can imply active participation or endorsement. Somewhat formal and literary.
彼は野党に与して政府を批判した。
He sided with the opposition and criticized the government.
その計画に与する者は少なかった。
Few people supported that plan.