A determinant is a factor or cause that makes something happen or leads directly to a decision.
The word determinant hasn't strayed much from its roots in the Latin word for "determining." As a noun or adjective, it refers to determining or deciding something. A snowstorm could be a determinant in school being canceled. Or a good health-care plan could be the determinant in someone taking a job. The determinant cause of a disease is responsible for the spread of the disease. Anything described as determinant is important.