obscaenus — de Vaan
obscaenus 'unpropitious, ill-omened; indecent' [adj. ο/ά] (P1.+; the second vowel vacillates between ae and e) Pit *skai-no- 'left, unpropitious'. PIE *skeh2-i-no- 'shaded; left'. IE cognates: see s.v. scaevus. Since e can be a phonetic development for ae in second syllable (*a/ > *e > ί) whereas ae cannot be explained if the original vowel was e, obscaenus must be the original form. EM propose to compare scaevus … — [de Vaan, s.v. obscaenus, p. 436]