noun, noun or participle which takes 'suru', intransitive verb
joining; becoming a member; subscription; signing up
Broadly used for joining a group, organization, or service, including clubs, insurance plans, treaties, and subscriptions. The verb form is 加入する (intransitive).
健康保険に加入する。
I enroll in health insurance.
彼
He joined a new club.
この条約に加入する国が増えている。
More countries are acceding to this treaty.