1.AdjectiveMaking good, thorough, or careful use of resources; not consuming extra. Especially, making good use of time or energy.
"An efficient process would automate all the routine work.; Our cleaners are almost too efficient: they throw away anything left out on a desk."
2.AdjectiveExpressing the proportion of consumed energy that was successfully used in a process; the ratio of useful output to total input.
"The motor is only 20% efficient at that temperature."
3.AdjectiveCausing effects, producing results; bringing into being; initiating change (rare except in philosophical and legal expression efficient cause = causative factor or agent).
"Ownership, maintenance, or use of the automobile need not be the direct and efficient cause of the injury sustained"