The Collaborative International Dictionary of English v.0.48:

Parameter \Pa*ram"e*ter\, n. [Pref. para- + -meter: cf. F.
   param[`e]tre.]
   1. A constant number which is part of a theory, function, or
      calculation, whose value is not determined by the form of
      the theory or equation itself, and may in some cases be
      arbitrary assigned.
      [PJC]

   2. Specifically:
      (a) (Math.) A term applied to some characteristic
          magnitude whose value, invariable as long as one and
          the same function, curve, surface, etc., is
          considered, serves to distinguish that function,
          curve, surface, etc., from others of the same kind or
          family. --Brande & C.
      (b) (Conic Sections) (in the ellipse and hyperbola), a
          third proportional to any diameter and its conjugate,
          or in the parabola, to any abscissa and the
          corresponding ordinate.
          [1913 Webster]

   Note: The parameter of the principal axis of a conic section
         is called the latus rectum.
         [1913 Webster]

   3. (Science) Any constant number which is required to
      calculate values of observed phenomena according to a
      theory, but the value of which must be determined by
      experiment, and cannot be calculated from the fundamental
      assumptions of the theory. In general, a theory which has
      a large number of parameters, though it may accurately
      predict experimental results, is considered as having less
      explanatory power and as being less esthetically pleasing
      than a theory with fewer parameters.
      [PJC]

   4. (Crystallog.) The ratio of the three crystallographic axes
      which determines the position of any plane; also, the
      fundamental axial ratio for a given species.
      [1913 Webster]

   5. The limits, guidelines, or assumptions from within which
      an activity is carried out; as, new arrivals need to learn
      the parameters of the research in our department.
      [PJC]

   6. (Computers) A variable used in a calculation within a
      computer program which must be assigned a value before the
      calculation can be performed; as, let's plug in the
      parameters and see what the result is.
      [PJC]

   7. A characteristic or element, especially one used as a
      criterion for evaluation or judgment; as, a useful
      parameter for determining efficiency.
      [PJC]

WordNet (r) 3.0 (2006):

parameter
    n 1: a constant in the equation of a curve that can be varied to
         yield a family of similar curves [syn: parameter,
         parametric quantity]
    2: any factor that defines a system and determines (or limits)
       its performance
    3: (computer science) a reference or value that is passed to a
       function, procedure, subroutine, command, or program [syn:
       argument, parameter]
    4: a quantity (such as the mean or variance) that characterizes
       a statistical population and that can be estimated by
       calculations from sample data

Moby Thesaurus II by Grady Ward, 1.0:

74 Moby Thesaurus words for "parameter":
   barometer, boundaries, boundary condition, bounds, bourns, canon,
   catch, check, circumference, circumscription, clause, compass,
   condition, confines, coordinates, criterion, degree, donnee, edges,
   escalator clause, escape clause, escape hatch, fine print, fringes,
   gauge, given, graduated scale, grounds, joker, kicker, limitations,
   limiting condition, limits, marches, measure, metes,
   metes and bounds, model, norm, obligation, outlines, outskirts,
   pale, parameters, pattern, perimeter, periphery, prerequisite,
   provision, provisions, proviso, quantity, reading, readout,
   requisite, rule, saving clause, scale, sine qua non, skirts,
   small print, specification, standard, stipulation, string, terms,
   test, touchstone, type, ultimatum, value, verges, whereas,
   yardstick



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

formal argument
param
parameter

    (Or "parameter") A name in a function or
   subroutine definition that is replaced by, or bound to, the
   corresponding actual argument when the function or
   subroutine is called.  In many languages formal arguments
   behave like local variables which get initialised on entry.

   See: argument.

   (2002-07-02)