Answer:
Antonyms: immature and full-grown
Explanation:
Antonyms are words that have opposite meanings to each other.
The definitions below are according to Oxford's dictionary
immature:
1. Not fully developed
2. having or showing an emotional or intellectual development appropriate to someone younger.
full-grown:
1. having reached maturity
The words immature and full-grown have directly opposite meanings, therefore they are antonyms
On the other hand, synonyms are words that have similar or very closely related meanings.
