Stifening or Stiffening: How To spell?
The word Stifening is misspelled against Stiffening, a noun meaning "Act or process of making stiff."
Stiffening has double "ff" is mispronounced as "f"Remember double 'FF' in between the strings Sti & ening which should not be misspelled with single 'F'
Wrong Spelling:  Sti-f-ening  Correct Spelling:  Sti-ff-ening 
Find more wrongly spelled words of Stiffening to spell it well.