Longtime (adjective)

1. Extending or continuing for a long period of time.
2. Having a history or relationship that dates back a long time.
3. Being a frequent or regular participant for a long period of time.

Origin:

From long + time.

Examples:

1. She was a longtime friend of the family.
2. He was a longtime resident of the city.
3. She has been a longtime supporter of the charity.
4. The company has been a longtime provider of quality products.
5. He was a longtime member of the club.