WordNet sense 1 (lowered in pitch by one chromatic semitone):

flat

WordNet sense 2 (raised in pitch by one chromatic semitone):

sharp

WordNet sense 3 (not existing in nature or subject to explanation according to natural laws; not physical or material):

supernatural

WordNet sense 4 (contrived by art rather than nature):

artificial

WordNet sense 5 (not in accordance with or determined by nature; contrary to nature):

unnatural