Ominous a. : Of or pertaining to an omen or to omens; being or exhibiting an omen; significant; portentous; -- formerly used both in a favorable and unfavorable sense; now chiefly in the latter; foreboding or foreshowing evil; inauspicious; as, an ominous dread.

Example:
What are some fast-paced, thunderous, eerie, Ominous, scary classical music pieces?

Taxonomy
Merriam-Webster Online Dictionary, Dictionary, webster, evil, Word Games, Webster Online Dictionary with audio pronunciations, thesaurus, glossary, english, language, ESL, Search, ä, adjective, omen, foreboding, ly, adverb.

Defination from the web:
ominous from the Merriam-Webster Online Dictionary with audio pronunciations, thesaurus, Word of the Day, and word games. ... synonyms ominous, portentous, fateful mean having a menacing or threatening aspect. ...