making good, thorough, or careful use of resources; not consuming extra. Especially, making good use of time or energy
expressing the proportion of consumed energy that was successfully used in a process; the ratio of useful output to total input
causing effects, producing results; bringing into being; initiating change (rare except in philosophical and legal expression efficient cause = causative factor or agent)
effective, efficacious
Having or showing skill; skillful.
Requiring special abilities or training.