Commutative

[kə'mjuːtətɪv;'kɒmjʊ,tətɪv] or [kə'mjutətɪv]

(adj.) (of a binary operation) independent of order; as in e.g. 'a x b = b x a' .

Checked by Joy--From WordNet

(a.) Relative to exchange; interchangeable; reciprocal.

Checked by Jerome