noun
formative period; formative years
Refers to a developmental stage when something (e.g., a nation, personality, or skill) takes shape. Often used in historical, psychological, or educational contexts.
この国は形成期に多くの困難を経験した。
This country experienced many hardships during its formative period.
幼少期は人格の形成期として重要だ。
Early childhood is important as a formative period for personality.
Compound of 形成 (formation) + 期 (period). The exact historical derivation is uncertain, but the meaning is transparent from its components.