The Collaborative International Dictionary of English v.0.48:

Heuristic \Heu*ris"tic\ (h[-u]*r[i^]s"t[i^]k), n.
   1. A heuristic method; a specific heuristic procedure.
      [PJC]

   2. A theory or approach which serves to promote discovery or
      learning by encouraging experimentation.
      [PJC]

The Collaborative International Dictionary of English v.0.48:

Heuristic \Heu*ris"tic\ (h[-u]*r[i^]s"t[i^]k), a. [Gr.
   e"yri`skein to discover.]
   1. Serving to promote discovery or learning; -- used
      especially of thories or paradigms which stimulate new
      ideas for discovering facts in experimental sciences.
      [1913 Webster +PJC]

   2. Serving to stimulate people to learn and discover on their
      own, especially by encouraging experimental and
      trial-and-error methods for solving problems.
      [PJC]

   3. Pertaining to or based on trial-and-error and experimental
      methods of learning and evaluation.
      [PJC]

   4. (Computers) Based on the use of an efficient trial-and
      error method to search a space of possible solutions to a
      problem, or to find an acceptable approximate solution,
      when an exact algorithmic method is unavailable or too
      time-consuming.
      [PJC]

WordNet (r) 3.0 (2006):

heuristic
    adj 1: of or relating to or using a general formulation that
           serves to guide investigation [ant: algorithmic]
    n 1: a commonsense rule (or set of rules) intended to increase
         the probability of solving some problem [syn: heuristic,
         heuristic rule, heuristic program]

Moby Thesaurus II by Grady Ward, 1.0:

34 Moby Thesaurus words for "heuristic":
   analytic, cut-and-try, empirical, examinational, examinatorial,
   examining, experimental, explorational, explorative, exploratory,
   fact-finding, feeling, groping, hit-or-miss, indagative,
   inspectional, inspectorial, investigational, investigative,
   investigatory, pilot, probationary, probative, probatory, proving,
   provisional, tentative, test, testing, trial, trial-and-error,
   trying, verificatory, zetetic



The Free On-line Dictionary of Computing (30 December 2018):

heuristic
non-algorithmic procedure

   1.  A rule of thumb, simplification, or educated
   guess that reduces or limits the search for solutions in
   domains that are difficult and poorly understood.  Unlike
   algorithms, heuristics do not guarantee optimal, or even
   feasible, solutions and are often used with no theoretical
   guarantee.

   2.  approximation algorithm.

   (2001-04-12)