The best replacement for introduction is preface.

The best alternatives to introduction are rated as following:
★★★★★  preface
★★★★  abstract
★★  background
★★  thesis
★★  prologue
★★  executive summary
★★  conclusion
★  overview
★  exposition
★  cover letter
★  introductory
★  forward
★  background of the study
★  foreword
★  literature review
★  abstract first
  segway
  abstract apa
  acknowledgement
  thesis statement
  rationale
  letter of intent
  background first

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★★★★★ thesis statement
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