causing effects, producing results; bringing into being; initiating change (rare except in philosophical and legal expression efficient cause = causative factor or agent)
expressing the proportion of consumed energy that was successfully used in a process; the ratio of useful output to total input
making good, thorough, or careful use of resources; not consuming extra. Especially, making good use of time or energy
effective, efficacious
That operates to produce an effect.
Any of a class of behaviors that produce consequences by operating (i.e., acting) upon the environment.
An operative person or thing.