The Collaborative International Dictionary of English v.0.48:

Matronymic \Mat`ro*nym"ic\, n. [L. mater mother + -nymic, as in
   patronimic.]
   See Metronymic.
   [1913 Webster]

WordNet (r) 3.0 (2006):

matronymic
    n 1: a name derived from the name of your mother or a maternal
         ancestor [syn: matronymic, metronymic]