Full-grown means having reached complete physical size and maturity. A full-grown golden retriever weighs around 70 pounds and stands about two feet tall at the shoulder, while a full-grown Chihuahua might weigh only six pounds. A full-grown oak tree can tower 80 feet high, but when it was planted, it was just a tiny acorn.

The term applies to living things that have finished growing and reached their adult size. A full-grown person has stopped getting taller, a full-grown sunflower has reached its maximum height, and a full-grown butterfly has emerged from its chrysalis with wings fully expanded.

People often use this term when the difference between young and mature size is dramatic. A full-grown elephant seal can weigh 8,000 pounds, even though it weighed only 75 pounds at birth. When someone says “That's a full-grown bear,” they're emphasizing that it's not a cub anymore but a large, powerful adult.

The word doesn't necessarily mean old or elderly, just finished growing. A 25-year-old person and a 75-year-old person are both full-grown, even though one is much older.