unreliable vs used

unreliable

adj
  • Not reliable. 

used

adj
  • That is or has or have been used. 

  • Familiar through use; usual; accustomed. 

  • That has or have previously been owned by someone else. 

verb
  • To perform habitually; to be accustomed [to doing something]. 

How often have the words unreliable and used occurred in a corpus of books? (source: Google Ngram Viewer )