From Japanese-English FreeDict Dictionary ver. 0.1:
[ichi1] 俄 /(en)tʃˈaɪniːz(ja)lˈe̞tə/, 俄か /kˈä/, [ichi1] にわか /niwˈäkä/
1. (adjectival nouns or quasi-adjectives (keiyodoshi))
(nouns which may take the genitive case particle `no')
(noun (common) (futsuumeishi))
Note: word usually written using kana alonesudden, abrupt, unexpected, improvised, hasty, offhand
2. (noun (common) (futsuumeishi))
俄狂言
Note: abbreviation (sometimes 仁輪加 (ateji))
impromptu skit