The Collaborative International Dictionary of English v.0.48:

Symmetric \Sym*met"ric\, a.
   Symmetrical.
   [1913 Webster]

WordNet (r) 3.0 (2006):

symmetric
    adj 1: having similarity in size, shape, and relative position
           of corresponding parts [syn: symmetrical, symmetric]
           [ant: asymmetric, asymmetrical]

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

symmetric

    1. A relation R is symmetric if, for all x and
   y,

   	x R y  =>  y R x

   If it is also antisymmetric (x R y & y R x => x == y) then
   x R y => x == y, i.e. no two different elements are related.

   2. In linear algebra, a member of the tensor product of a
   vector space with itself one or more times, is symmetric if
   it is a fixed point of all of the linear isomorphisms of
   the tensor product generated by permutations of the ordering
   of the copies of the vector space as factors.  It is said to
   be antisymmetric precisely if the action of any of these
   linear maps, on the given tensor, is equivalent to
   multiplication by the sign of the permutation in question.

   (1996-09-22)