Antonyms for Sharp (opposite meaning)
WordNet sense 1 (lowered in pitch by one chromatic semitone):
flatWordNet sense 2 ((of a key) containing no sharps or flats; (of a note) being neither raised nor lowered by one chromatic semitone):
naturalWordNet sense 3 (not keenly felt):
dullFrom the ODE community, based on WordNetadd/edit