For subject specific encyclopedias or encyclopedia articles on feminism or issues regarding feminist theory, your best bet is to search through the SU Libraries' SUMMON database, using the term feminism or "feminist theory" and then refining the searchas a subject and to reference books as a "content type" and then limit to the newest sources.
CQ Researcher Plus Archive - An encyclopedia addressing national and global policy issues.
CREDO Reference - A collection of online reference books.
International Encyclopedia of the Social & Behavioral Sciences H41 .I58 2001 v. 1-26 REF
Routledge International Encyclopedia of Women HQ 1115 .R69 2000 v. 1-4 REF