for·ma·tive 
/ˈfoɚmətɪv/ adjective
/ˈfoɚmətɪv/ adjective [more formative; most formative] 1 — used to describe the time when someone or something is growing or being formed ▪ The movement was then still in its formative stages. ▪ His family traveled widely during his formative years. [=when he was young] 2 : helping to develop something
▪ This experience had a formative influence on his art. ▪ a formative experience
▪ This experience had a formative influence on his art. ▪ a formative experience
