efficient
adjective
°Making 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."
°Using a particular proportion of available energy.
"The motor is only 20% efficient at that temperature."

efficacy
noun
°Ability to produce a desired amount of a desired effect.
synonyms: efficacity

efficiency
noun
°The extent to which time is well used for the intended task.
"The efficiency of the planning department is deplorable."
°The extent to which a resource, such as electricity, is used for the intended purpose.
"The efficiency of this loudspeaker is 40%."
synonyms: effectiveness


effectiveness
noun
°The property of being effective.
°The ability to be effective.