trepidation vs unconfidence

trepidation

noun
  • A fearful state; a state of concern or hesitation. 

  • An involuntary trembling, sometimes an effect of paralysis, but usually caused by terror or fear. 

unconfidence

noun
  • Absence of confidence; uncertainty; doubt. 

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