tabula : Idioms & Phrases

• noun a young mind not yet affected by experience (according to John Locke)
  
• noun an opportunity to start over without prejudice
  fresh start; clean slate.
  

WordNet

• L., a smoothed tablet; hence, figuratively, the mind in its earliest state, before receiving impressions from without; a term used by Hobbes, Locke, and others, in maintaining a theory opposed to the doctrine of innate ideas.

Webster 1913