noun
Refers to the role or contribution someone or something plays in a particular situation. Often used with verbs like 買う (to take on a role) or 果たす (to fulfill a role).
彼はプロジェクトで重要な一役を買った。
He took on an important role in the project.
この発明は
This invention is playing a part in technological progress.
役割 is a more general and common word for 'role' or 'function'. 一役 emphasizes a specific contribution or part played in a particular context, often with a nuance of being one part among others.
Compound of 一 (one) and 役 (role, duty).