leading force; driving force; leader
Refers to a person, group, or thing that plays a central role in pulling an effort forward, like a driving force or key leader in a project, movement, or team.
He played an active role as the driving force behind the project.
This new technology will likely become the leading force in the industry.
Compound of 牽引 (けんいん, 'traction, pulling') and 役 (やく, 'role'). The kanji 牽 means 'pull, tug', 引 means 'pull, draw', and 役 means 'role, duty'.