The Collaborative International Dictionary of English v.0.48:

Efficiently \Ef*fi"cient*ly\, adv.
   With effect; effectively.
   [1913 Webster]

WordNet (r) 3.0 (2006):

efficiently
    adv 1: with efficiency; in an efficient manner; "he functions
           efficiently" [syn: efficiently, expeditiously] [ant:
           inefficiently]

Moby Thesaurus II by Grady Ward, 1.0:

47 Moby Thesaurus words for "efficiently":
   ably, adeptly, adequately, adroitly, advantageously, agilely,
   aptly, artfully, artistically, brilliantly, capably, cleverly,
   competently, conveniently, cunningly, deftly, dexterously,
   dextrously, effectively, effectually, excellently, expertly,
   featly, functionally, handily, ingeniously, masterfully, neatly,
   nimbly, practically, proficiently, profitably, resourcefully,
   serviceably, skillfully, spryly, superbly, to advantage,
   to good effect, to good use, to profit, usefully, well,
   with consummate skill, with finesse, with genius, with skill