Subscriber (noun)

1. A person who has signed up to receive or access something on a regular basis, such as a publication or service.
2. A person who has made a commitment to support or contribute to something, such as a cause or organization.
3. A person who has agreed to a proposal or statement, such as in a legal or political context.

Origin:

From latin subscribere, 'to write underneath'.

Examples:

1. She became a subscriber to the monthly magazine for her son.
2. He became a subscriber to the streaming service to watch movies and TV shows.
3. She became a subscriber to the cause and made a monthly donation.
4. He became a subscriber to the treaty and promised to follow its provisions.
5. They became subscribers to the proposal and promised to work together to implement it.