Milennial or Millennial: How To spell?
The word Milennial is misspelled against Millennial, an adjective meaning "pertaining to the millennium, to a thousand years; as, a millennial period; millennial happiness."
Millennial has double "ll" is mispronounced as "l"Remember double 'LL' in between the strings mi & ennial which should not be misspelled with single 'L'
Wrong Spelling:  mi-l-ennial  Correct Spelling:  mi-ll-ennial 
Find more wrongly spelled words of Millennial to spell it well.