Pronunciation: [smˈɑːtɪəst] (IPA)
Correct spelling for the English word "smartiest" is [smˈɑːtɪəst], [smˈɑːtɪəst], [s_m_ˈɑː_t_ɪ__ə_s_t] (IPA phonetic alphabet).
Correct spelling for smartiest