[1] : The Collaborative International Dictionary of English v.0.48

efficient \effi"cient\ e^ffi^sh"ent, a. l. efficiens,
   -entis, p. pr. of efficere to effect: cf. f. efficient. see
   effect, n.
   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.
   1913 webster

         the efficient cause is the working cause. --wilson.

   syn: effective; effectual; competent; able; capable;
        material; potent.
        1913 webster
see also:
effect 

[2] : The Collaborative International Dictionary of English v.0.48

efficient \effi"cient\, n.
   an efficient cause; a prime mover.
   1913 webster

         god . . . moveth mere natural agents as an efficient
         only.                                    --hooker.
   1913 webster

[3] : WordNet (r) 2.0

efficient
     adj 1: being effective without wasting time or effort or expense;
            "an efficient production manager"; "efficient engines
            save gas" ant: inefficient
     2: 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" syn:
        effective
see also:
inefficient effective 

[4] : Moby Thesaurus II by Grady Ward, 1.0

39 moby thesaurus words for "efficient":
   able, active, adequate, au fait, banausic, capable, competent,
   economic, effective, effectual, efficacious, equal to, feasible,
   fit, fitted, fitted for, functional, go, journeyman, operable,
   operational, operative, practicable, practical, pragmatic,
   productive, proficient, qualified, realizable, suited, thrifty,
   unwasteful, up to, up to snuff, well-fitted, well-qualified,
   well-suited, workable, worthy

Efficient >> E Words
Efficient, definition of term: Efficient
efficient_pag1.html

Efficient Cause >> E Words
Efficient Cause, definition of term: Efficient Cause
efficient+cause_pag1.html