The Collaborative International Dictionary of English v.0.48:

Constructive \Con*struct"ive\, a. [Cf. F. constructif.]
   1. Having ability to construct or form; employed in
      construction; as, to exhibit constructive power.
      [1913 Webster]

            The constructive fingers of Watts.    --Emerson.
      [1913 Webster]

   2. Derived from, or depending on, construction, inference, or
      interpretation; not directly expressed, but inferred.
      [1913 Webster]

   3. helpful; promoting improvement; intended to help; as,
      constructive criticism; constructive suggestions.
      Contrasted with destructive.
      [PJC]

   Constructive crimes (Law), acts having effects analogous to
      those of some statutory or common law crimes; as,
      constructive treason. Constructive crimes are no longer
      recognized by the courts.

   Constructive notice, notice imputed by construction of law.


   Constructive trust, a trust which may be assumed to exist,
      though no actual mention of it be made.
      [1913 Webster]

WordNet (r) 3.0 (2006):

constructive
    adj 1: constructing or tending to construct or improve or
           promote development; "constructive criticism"; "a
           constructive attitude"; "a constructive philosophy";
           "constructive permission" [ant: destructive]
    2: emphasizing what is laudable or hopeful or to the good;
       "constructive criticism"

Moby Thesaurus II by Grady Ward, 1.0:

46 Moby Thesaurus words for "constructive":
   advantageous, aidful, beneficial, causative, conducive,
   construable, constructional, contributory, creative, deduced,
   definitional, demiurgic, derived, descriptive, diagnostic,
   exegetic, formative, furthersome, generative, good for, helpful,
   hermeneutic, implicit, inferential, inferred, interpretable,
   interpretational, interpretive, inventive, originative, positive,
   practicable, practical, productive, profitable, ratiocinative,
   remedial, renderable, salutary, semeiological, serviceable,
   symptomatological, therapeutic, tropological, useful, virtual



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

CONSTRUCTIVE. That which is interpreted.
     2. Constructive presence. The commission of crimes, is, when a party is
not actually present, an eyewitness to its commission but, acting with
others, watching while another commits the crime. 1 Russ. Cr. 22.
     3. Constructive larceny. One where the taking was not apparently
felonious, but by construction of the prisoner's acts it is just to presume
he intended at the time of taking to appropriate the property feloniously to
his own use; 2 East, P. C. 685; 1 Leach, 212; as when he obtained the
delivery of the goods animo furandi. 2 N. & M. 90. See 15 S. & R. 93; 4
Mass. 580; I Bay, 242.
     4. Constructive breaking into a house. In order to commit a burglary,
there must be a breaking of the house; this may be actual or constructive. A
constructive breaking is when the burglar gains an entry into the house by
fraud, conspiracy, or threat. See Burglary, A familiar instance of
constructive breaking is the case of a burglar who coming to the house under
pretence of business, gains admittance, and after being admitted, commits
such acts as, if there had been an actual brooking, would have amounted to a
burglary Bac. Ab. Burglary, A. See 1 Moody Cr. Cas. 87, 250.
     5. Constructive notice. Such a notice, that although it be not actual,
is sufficient in law; an example of this is the recording of a deed, which
is notice to all the world, and so is the pendancy of a suit a general
notice of an equity. 4 Bouv. Inst. n. 3874. See Lis pendens.
     6. Constructive annexation. The annexation to the inheritance by the
law, of certain things which are not actually attached to it; for example,
the keys of a house; and heir looms are constructively annexed. Shep. Touch.
90; Poth. Traits des Choses, Sec. 1.
     7. Constructive fraud. A contract or act, which, not originating in
evil design and contrivance to perpetuate a positive fraud or injury upon
other persons, yet, by its necessary tendency to deceive or mislead them, or
to violate a public or private confidence, or to impair or injure public
interest, is deemed equally reprehensible with positive fraud, and therefore
is prohibited by law, as within the same reason and mischief as contracts
and acts done malo animo. 1 Story, Eq. Sec. 258 to 440.