Vocabulary with easy examples http://www.skonline.org/website/mathonline/mathvocab.htm
Math Dictionary with pictures and examples http://www.mathsisfun.com/definitions/letter-a.html
A math dictionary for kids http://www.amathsdictionaryforkids.com/
A regular dictionary with all the words. http://www.dictionary.com
This is a very good math vocabulary site. http://www.mathwords.com/