Duodecenial or Duodecennial: How To spell?
The word Duodecenial is misspelled against Duodecennial, an adjective meaning "Consisting of twelve years."
Duodecennial has double "nn" is mispronounced as "n"Remember double 'NN' in between the strings duodece & ial which should not be misspelled with single 'N'
Wrong Spelling:  duodece-n-ial  Correct Spelling:  duodece-nn-ial 
Check more misspelled words of Duodecennial to spell it correct.