The Collaborative International Dictionary of English v.0.48:
Gynarchy \Gyn"ar*chy\ (j[i^]n"[.a]r*k[y^]), n. [Gr. gynh` a woman + -archy.] Government by a woman. --Chesterfield. [1913 Webster]WordNet (r) 3.0 (2006):
gynarchy n 1: a political system governed by a woman [syn: gynecocracy, gynarchy]