The Collaborative International Dictionary of English v.0.48:

Beneficial \Ben`e*fi"cial\, a. [Cf. F. b['e]n['e]ficial, LL.
   beneficialis.]
   1. Conferring benefits; useful; profitable; helpful;
      advantageous; serviceable; contributing to a valuable end;
      -- followed by to.
      [1913 Webster]

            The war which would have been most beneficial to us.
                                                  --Swift.
      [1913 Webster]

   2. (Law) Receiving, or entitled to have or receive,
      advantage, use, or benefit; as, the beneficial owner of an
      estate. --Kent.
      [1913 Webster]

   3. King. [Obs.] "A beneficial foe." --B. Jonson.
      [1913 Webster]

   Syn: See Advantage.
        [1913 Webster]

WordNet (r) 3.0 (2006):

beneficial
    adj 1: promoting or enhancing well-being; "an arms limitation
           agreement beneficial to all countries"; "the beneficial
           effects of a temperate climate"; "the experience was good
           for her" [syn: beneficial, good]

Moby Thesaurus II by Grady Ward, 1.0:

80 Moby Thesaurus words for "beneficial":
   advantageous, aidful, appropriate, auspicious, banausic,
   benevolent, benign, bon, bonny, bracing, braw, bueno, capital,
   cogent, commendable, commodious, conducive, constitutional,
   constructive, contributory, effective, efficacious, elegant,
   employable, estimable, excellent, expedient, fair, famous,
   favorable, fine, fitting, functional, furthersome, good, good for,
   goodly, grand, health-enhancing, health-preserving, healthful,
   healthy, helpful, hygeian, hygienic, invigorating, kind, laudable,
   nice, noble, of general utility, of help, of service, of use,
   pleasant, positive, practical, pragmatical, profitable, proper,
   refreshing, regal, remedial, royal, salubrious, salutary, sanitary,
   serviceable, skillful, sound, splendid, supportive, therapeutic,
   tonic, useful, utilitarian, valid, very good, virtuous,
   wholesome



Bouvier's Law Dictionary, Revised 6th Ed (1856):

BENEFICIAL. Of advantage, profit or interest; as the wife has a beneficial
interest in property held by a trustee for her. Vide Cestui que trust.