Formative (adjective)

1. Relating to the formation or development of something.
2. Having a strong influence on shaping the character or development of a person or thing.

Origin:

From the latin word "formare" meaning to form or shape.

Examples:

1. Formative years are very important in the development of a child.
2. Formative assessment is used to evaluate students' progress.
3. The formative experiences helped shape the person he is today.
4. The formative feedback helped the team improve their performance.
5. The formative years in the company were crucial to its success.