effectiveness
(n) : the property of being effective; the degree to which something is effective
"he questioned the effectiveness of the treatment."
efficacity
(n) : efficacy
efficiency
(n) : the extent to which time is well used for the intended task; the extent to which a resource, such as electricity, is used for the intended purpose
"the efficiency of the planning department is deplorable."
efficacy
(n) : ability to produce a desired amount of a desired effect; efficiency; effectiveness
synonyms: efficacity
efficient
(adj) : making good, thorough, or careful use of resources; not consuming extra. Especially, making good use of time or energy; using a particular proportion of available energy
"an efficient process would automate all the routine work."