Encyclopedias, dictionaries, and other resources to help you discover basic information—names, dates, definitions, summaries, etc. These are good places to start when narrowing or choosing your topic, and when beginning research on an unfamiliar subject.
Current Mathematical Publications (CMP) is a subject index of bibliographic data for recent and forthcoming publications. Updated daily on MathSciNet. (Most items are later reviewed in MR. All items in MR appear first in CMP. The MR record for an item with a review replaces the CMP record for that item.)
CRC Concise Encyclopedia of Mathematics by 
Encyclopaedia of Mathematics by 
Encyclopedic Dictionary of Mathematics by 
Mathematics Dictionary by 
Notable Women in Mathematics by 