The Collaborative International Dictionary of English v.0.48:

Polymorphism \Pol`y*mor"phism\, n.
   1. (Crystallog.) Same as Pleomorphism.
      [1913 Webster]

   2. (Biol.)
      (a) The capability of assuming different forms; the
          capability of widely varying in form.
      (b) Existence in many forms; the coexistence, in the same
          locality, of two or more distinct forms independent of
          sex, not connected by intermediate gradations, but
          produced from common parents.
          [1913 Webster]

WordNet (r) 3.0 (2006):

polymorphism
    n 1: (genetics) the genetic variation within a population that
         natural selection can operate on
    2: (chemistry) the existence of different kinds of crystal of
       the same chemical compound [syn: polymorphism,
       pleomorphism]
    3: (biology) the existence of two or more forms of individuals
       within the same animal species (independent of sex
       differences)

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

polymorphism
polymorphic

    The ability to leave parts of a type in a
   typed language unspecified.  The term has three distinct uses:

   * Parametric polymorphism refers to the use of type variables in
   a strongly typed language.

   * Overloading, sometimes called ad-hoc polymorphism, means
   using the same syntax for different types.

   * object-oriented polymorphism allows a variable to refer
   to objects whose class is not known at compile time.

   (2014-01-05)