Bisextile or Bissextile: How To spell?
The word Bisextile is misspelled against Bissextile, a noun meaning "Leap year; every fourth year, in which a day is added to the month of February on account of the excess of the tropical year (365 d. 5 h. 48 m. 46 s.) above 365 days. But one day added every four years is equivalent to six hours each year, which is 11 m. 14 s. more than the excess of the real year. Hence, it is necessary to suppress the bissextile day at the end of every century which is not divisible by 400, while it is retained at the end of those which are divisible by 400."
Bissextile has double "ss" is mispronounced as "s"Remember double 'SS' in between the strings bi & extile which should not be misspelled with single 'S'
Wrong Spelling:  bi-s-extile  Correct Spelling:  bi-ss-extile 
Find more wrongly spelled words of Bissextile to spell it well.