EFFICIENT

effective, efficient

(adjective) able to accomplish a purpose; functioning effectively; “people who will do nothing unless they get something out of it for themselves are often highly effective persons...”-G.B.Shaw; “effective personnel”; “an efficient secretary”; “the efficient cause of the revolution”

efficient

(adjective) being effective without wasting time or effort or expense; “an efficient production manager”; “efficient engines save gas”

Source: WordNet® 3.1

Etymology

Adjective

efficient (comparative more efficient, superlative most efficient)

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)

(proscribed, old use) effective

Usage notes

Webster's Revised Unabridged Dictionary from 1913 still lists efficient and effective as synonyms, but all major dictionaries now show that these words now only have different meanings in careful use. Use of both for the other meaning is however widespread enough that Longman's Exam Dictionary, for example, finds it necessary to proscribe the use of one for the other with several examples at each entry and provides the following summary

• efficient (“working quickly and without waste”)

• effective (“having the desired effect”)

Antonyms

• inefficient

Noun

efficient (plural efficients)

(obsolete) a cause; something that causes an effect

Source: Wiktionary

Ef*fi"cient, a. Etym: [L. efficiens, -entis, p. pr. of efficere to effect: cf. F. efficient. See Effect, n.]

Definition: Causing effects; producing results; that makes the effect to be what it is; actively operative; not inactive, slack, or incapable; characterized by energetic and useful activity; as, an efficient officer, power. The efficient cause is the working cause. Wilson.

Syn.

– Effective; effectual; competent; able; capable; material; potent.

Ef*fi"cient, n.

Definition: An efficient cause; a prime mover. God . . . moveth mere natural agents as an efficient only. Hooker.

Source: Webster’s Unabridged Dictionary 1913 Edition