Wordnet 3.0
NOUN (1)
1. 
 (Judaism) an ancient commentary on part of the Hebrew scriptures that is based on Jewish methods of interpretation and attached to the biblical text; 
The Collaborative International Dictionary of English v.0.48:
Midrash \Mid*rash"\, n.; pl. Midrashim, Midrashoth. [Heb.,
   explanation.]
   A talmudic exposition of the Hebrew law, or of some part of
   it.
   [1913 Webster]
WordNet (r) 3.0 (2006):
Midrash
    n 1: (Judaism) an ancient commentary on part of the Hebrew
         scriptures that is based on Jewish methods of
         interpretation and attached to the biblical text