Correct spelling for the English word "Decennovary" is [dɪsˈɛnəvəɹi], [dɪsˈɛnəvəɹi], [d_ɪ_s_ˈɛ_n_ə_v_ə_ɹ_i] (IPA phonetic alphabet).
Pert. to the number nineteen; designating a period or circle of nineteen years.
Etymological and pronouncing dictionary of the English language. By Stormonth, James, Phelp, P. H. Published 1874.