Source : Webster's Revised Unabridged Dictionary (1913)

Peanut butter \Pea"nut but"ter\
   A paste made by mixing ground fresh roasted peanuts with a
   small quantity of water or oil, and used chiefly as a relish
   on sandwiches, etc.

Source : WordNet®

peanut butter
     n : a spread made from ground peanuts